Engineered particles and methods of use

ABSTRACT

Engineered particles are provided may be used for the delivery of a bioactive agent to the respiratory tract of a patient. The particles may be used in the form of dry powders or in the form of stabilized dispersions comprising a nonaqueous continuous phase. In particularly preferred embodiments the particles may be used in conjunction with an inhalation device such as a dry powder inhaler, metered dose inhaler or a nebulizer.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of PCT Application No.US98/20602, filed Sep. 29, 1998, which is a continuation-in-part ofpending U.S. patent application Ser. No. 09/133,848, filed Aug. 14,1998, which is a continuation-in-part of pending U.S. patent applicationSer. No. 09/106,932 filed Jun. 29, 1998 which claims priority from U.S.Provisional Application Ser. No. 60/060,337, filed Sep. 29, 1997 and nowlapsed.

FIELD OF THE INVENTION

The present invention relates to formulations and methods for theproduction of perforated microstructures which comprise an active agent.In particularly preferred embodiments, the active agent will comprise abioactive agent. The perforated microstructures will preferably be usedin conjunction with inhalation devices such as a metered dose inhaler,dry powder inhaler or nebulizer for both topical and systemic deliveryvia pulmonary or nasal routes.

BACKGROUND OF THE INVENTION

Targeted drug delivery means are particularly desirable where toxicityor bioavailability of the pharmaceutical compound is an issue. Specificdrug delivery methods and compositions that effectively deposit thecompound at the site of action potentially serve to minimize toxic sideeffects, lower dosing requirements and decrease therapeutic costs. Inthis regard, the development of such systems for pulmonary drug deliveryhas long been a goal of the pharmaceutical industry.

The three most common systems presently used to deliver drugs locally tothe pulmonary air passages are dry powder inhalers (DPIs), metered doseinhalers (MDIs) and nebulizers. MDIs, the most popular method ofinhalation administration, may be used to deliver medicaments in asolubilized form or as a dispersion. Typically MDIs comprise a Freon orother relatively high vapor pressure propellant that forces aerosolizedmedication into the respiratory tract upon activation of the device.Unlike MDIs, DPIs generally rely entirely on the patient's inspiratoryefforts to introduce a medicament in a dry powder form to the lungs.Finally, nebulizers form a medicament aerosol to be inhaled by impartingenergy to a liquid solution. More recently, direct pulmonary delivery ofdrugs during liquid ventilation or pulmonary lavage using afluorochemical medium has also been explored. While each of thesemethods and associated systems may prove effective in selectedsituations, inherent drawbacks, including formulation limitations, canlimit their use.

The MDI is dependent on the propulsive force of the propellant systemused in its manufacture. Traditionally, the propellant system hasconsisted of a mixture of chlorofluorocarbons (CFCs) which are selectedto provide the desired vapor pressure and suspension stability.Currently, CFCs such as Freon 11, Freon 12, and Freon 114 are the mostwidely used propellants in aerosol formulations for inhalationadministration.: While such systems may be used to deliver solubilizeddrug, the selected bioactive agent is typically incorporated in the formof a fine particulate to provide a dispersion. To minimize or preventthe problem of aggregation in such systems, surfactants are often usedto coat the surfaces of the bioactive agent and assist in wetting theparticles with the aerosol propellant. The use of surfactaits in thisway to maintain substantially uniform dispersions is said to “stabilize”the suspensions.

Unfortunately, traditional chlorofluorocarbon propellants are nowbelieved to deplete stratospheric ozone and, as a consequence, are beingphased out. This, in turn, has led to the development of aerosolformulations for pulmonary drug delivery employing so-calledenvironmentally friendly propellants. Classes of propellants which arebelieved to have minimal ozone-depletion potential in comparison withCFCs are perfluorinated compounds (PFCs) and hydrofluoroalkanes (HFAs).While selected compounds in these classes may function effectively asbiocompatible propellants, many of the surfactants that were effectivein stabilizing drug suspensions in CFCs are no longer effective in thesenew propellant systems. As the solubility of the surfactant in the HFAdecreases, diffusion of the surfactant to the interface between the drugparticle and HFA becomes exceedingly slow, leading to poor wetting ofthe medicament particles and a loss of suspension stability. Thisdecreased solubility for surfactants in HFA propellants is likely toresult in decreased efficacy with regard to any incorporated bioactiveagent.

More generally, drug suspensions in liquid fluorochemicals, includingHFAs, comprise heterogeneous systems which usually require redispersionprior to use. Yet, because of factors such as patient complianceobtaining a relatively homogeneous distribution of the pharmaceuticalcompound is not always easy or successful. In addition, prior artformulations comprising micronized particulates may be prone toaggregation of the particles which can result in inadequate delivery ofthe drug. Crystal growth of the suspensions via Ostwald ripening mayalso lead to particle size heterogeneity and can significantly reducethe shelf-life of the formulation. Another problem with conventionaldispersions comprising micronized dispersants is particle coarsening.Coarsening may occur via several mechanisms such as flocculation,fusion, molecular diffusion, and coalescence. Over a relatively shortperiod of time these processes can coarsen the formulation to the pointwhere it is no longer usable. As such, while conventional systemscomprising fluorochemical suspensions for MDIs or liquid ventilation arecertainly a substantial improvement over prior art non-fluorochemicaldelivery vehicles, the drug suspensions may be improved upon to enableformulations with improved stability that also offer more efficient andaccurate dosing at the desired site.

Similarly, conventional powdered preparations for use in DPIs often failto provide accurate, reproducible dosing over extended periods. In thisrespect, those skilled in the art will appreciate that conventionalpowders (i.e. micronized) tend to aggregate due to hydrophobic orelectrostatic interactions between the fine particles. These changes inparticle size and increases in cohesive forces over time tend to providepowders that give undesirable pulmonary distribution profiles uponactivation of the device. More particularly, fine particle aggregationdisrupts the aerodynamic properties of the powder, thereby preventinglarge amounts of the aerosolized medicament from reaching the deeperairways of the lung where it is most effective.

In order to overcome the unwanted increases in cohesive forces, priorart formulations have typically used large carrier particles comprisinglactose to prevent the fine drug particles from aggregating. Suchcarrier systems allow for at least some of the drug particles to looselybind to the lactose surface and disengage upon inhalation. However,substantial amounts of the drug fail to disengage from the large lactoseparticles and are deposited in the throat. As such, these carriersystems are relatively inefficient with respect to the fine particlefraction provided per actuation of the DPI. Another solution to particleaggregation is proposed in WO 98/31346 wherein particles havingrelatively large geometric diameters (i.e. preferably greater than 10μm) are used to reduce the amount of particle interactions therebypreserving the flowability of the powder. As with the prior art carriersystems, the use of large particles apparently reduces the overallsurface area of the powder preparation reportedly resulting inimprovements in flowability and fine particle fraction. Unfortunately,the use of relatively large particles may result in dosing limitationswhen used in standard DPIs and provide for less than optimal dosing dueto the potentially prolonged dissolution times. As such, there stillremains a need for standard sized particles that resist aggregation andpreserve the flowability and dispersibility of the resulting powder.

Accordingly, it is an object of the present invention to provide methodsand preparations that advantageously allow for the nasal or pulmonaryadministration of powders having relatively high fine particlefractions.

It is a further object of the present invention to provide stabilizedpreparations suitable for aerosolization and subsequent administrationto the pulmonary air passages of a patient in need thereof.

It is yet another object of the present invention to provide powdersthat may be used to provide stabilized dispersions.

It is still a further object of the present invention to provide powdersexhibiting relatively low cohesive forces that are compatible for use indry powder inhalers.

SUMMARY OF THE INVENTION

These and other objects are provided for by the invention disclosed andclaimed herein. To that end, the methods and associated compositions ofthe present invention provide, in a broad aspect, for the improveddelivery of agents to a desired site. More particularly, the presentinvention may provide for the delivery of bioactive agents to selectedphysiological target sites using perforated microstructure powders. Inpreferred embodiments, the bioactive agents are in a form foradministration to at least a portion of the pulmonary air passages of apatient in need thereof. To that end, the present invention provides forthe formation and use of perforated microstructures and delivery systemscomprising such powders, as well as individual components thereof Thedisclosed powders may further be dispersed in selected suspension mediato provide stabilized dispersions. Unlike prior art powders ordispersions for drug delivery, the present invention preferably employsnovel techniques to reduce attractive forces between the particles. Assuch, the disclosed powders exhibit improved flowability anddispersibilty while the disclosed dispersions exhibit reduceddegradation by flocculation, sedimentation or creaming. Moreover, thestabilized preparations of the present invention preferably comprise asuspension medium (e.g. a fluorochemical) that further serves to reducethe rate of degradation with respect to the incorporated bioactiveagent. Accordingly, the dispersions or powders of the present inventionmay be used in conjunction with metered dose inhalers, dry powderinhalers, atomizers, nebulizers or liquid dose instillation (LDI)techniques to provide for effective drug delivery.

With regard to particularly preferred embodiments, the hollow and/orporous perforated microstructures substantially reduce attractivemolecular forces, such as van der Waals forces, which dominate prior artpowdered preparations and dispersions. In this respect, the powderedcompositions typically have relatively low bulk densities whichcontribute to the flowability of the preparations while providing thedesired characteristics for inhalation therapies. More particularly, theuse of relatively low density perforated (or porous) microstructures ormicroparticulates significantly reduces attractive forces between theparticles thereby lowering the shear forces and increasing theflowability of the resulting powders. The relatively low density of theperforated microstructures also provides for superior aerodynamicperformance when used in inhalation therapy. When used in dispersions,the physical characteristics of the powders provide for the formation ofstable preparations. Moreover, by selecting dispersion components inaccordance with the teachings herein, interparticle attractive forcesmay further be reduced to provide formulations having enhancedstability.

Accordingly, select embodiments of the invention provide for powdershaving increased dispersibility comprising a plurality of perforatedmicrostructures having a bulk density of less than about 0.5 g/cm³wherein said perforated microstructure powder comprises an active agent.

With regard to the perforated microstructures, those skilled in the artwill appreciate that they may be formed of any biocompatible materialproviding the desired physical characteristics or morphology. In thisrespect, the perforated microstructures will preferably comprise pores,voids, defects or other interstitial spaces that act to reduceattractive forces by minimizing surface interactions and decreasingshear forces. Yet, given these constraints, it will be appreciated thatany material or configuration may be used to form the microstructurematrix. As to the selected materials, it is desirable that themicrostructure incorporates at least one surfactant. Preferably, thissurfactant will comprise a phospholipid or other surfactant approved forpulmonary use. Similarly, it is preferred that the microstructuresincorporate at least one active agent which may be a bioactive agent. Asto the configuration, particularly preferred embodiments of theinvention incorporate spray dried, hollow microspheres having arelatively thin porous wall defining a large internal void, although,other void containing or perforated structures are contemplated as well.In preferred embodiments the perforated microstructures will furthercomprise a bioactive agent.

Accordingly, the present invention provides for the use of a bioactiveagent in the manufacture of a medicament for pulmonary delivery wherebythe medicament comprises a plurality of perforated microstructures whichare aerosolized using an inhalation device to provide aerosolizedmedicament comprising said bioactive agent wherein said aerosolizedmedicament is administered to at least a portion of the nasal orpulmonary air passages of a patient in need thereof.

It will further be appreciated that, in selected embodiments, thepresent invention comprises methods for forming perforatedmicrostructures that exhibit improved dispersibility. In this regard, itwill be appreciated that the disclosed perforated microstructures reduceattractive molecular forces, such as van der Waals forces, whichdominate prior art powdered preparations. That is, unlike prior artpreparations comprising relatively dense, solid particles or nonporousparticles (e.g. micronized), the powdered compositions of the presentinvention exhibit increased flowability and dispersibility due to thelower shear forces. In part, this reduction in cohesive forces is aresult of the novel production methods used to provide the desiredpowders.

As such, preferred embodiments of the invention provide methods forforming a perforated microstructure comprising the steps of:

-   -   providing a liquid feed stock comprising an active agent;    -   atomizing said liquid feed stock to produce dispersed liquid        droplets;    -   drying said liquid droplets under predetermined conditions to        form perforated microstructures comprising said active agent;        and    -   collecting said perforated microstructures.

With regard to the formation of the perforated microstructures it willbe appreciated that, in preferred embodiments, the particles will bespray dried using commercially available equipment. In this regard thefeed stock will preferably comprise a blowing agent that may be selectedfrom fluorinated compounds and nonfluorinated oils. Preferably, thefluorinated compounds will have a boiling point of greater than about60° C. Within the context of the instant invention the fluorinatedblowing agent may be retained in the perforated microstructures tofurther increase the dispersibility of the resulting powder or improvethe stability of dispersions incorporating the same. Further,nonfluorinated oils may be used to increase the solubility of selectedbioactive agents (e.g. steroids) in the feed stock, resulting inincreased concentrations of bioactive agents in the perforatedmicrostructures.

As discussed above, the dispersibility of the perforated microstructurepowders may be increased by reducing, or minimizing, the van der Waalsattractive forces between the constituent perforated microstructures. Inthis regard, the present invention further provides methods forincreasing the dispersibility of a powder comprising the steps of:

-   -   providing a liquid feed stock comprising an active agent; and    -   spray drying said liquid feed stock to produce a perforated        microstructure powder having a bulk density of less than about        0.5 g/cm³ wherein said powder exhibits reduced van der Waals        attractive forces when compared to a relatively non-porous        powder of the same composition. In particularly preferred        embodiments the perforated microstructures will comprise hollow,        porous microspheres.

The blowing agent may be dispersed in the carrier using techniques knownin the art for the production of homogenous dispersions such asonication, mechanical mixing or high pressure homogenization. Othermethods contemplated for the dispersion of blowing agents in the feedsolution include co-mixing of two fluids prior to atomization asdescribed for double nebulization techniques. Of course, it will beappreciated that the atomizer can be customized to optimize the desiredparticle characteristics such as particle size. In special cases adouble liquid nozzle may be employed. In another embodiment, the blowingagent may be dispersed by introducing the agent into the solution underelevated pressures such as in the case of nitrogen or carbon dioxidegas.

As to the delivery of perforated microstructure powders or stabilizeddispersions, another aspect of the present invention is directed toinhalation systems for the administration of one or more bioactiveagents to a patient. As such, the present invention provides systems forthe pulmonary administration of a bioactive agent to a patientcomprising:

-   -   an inhalation device comprising a reservoir; and    -   a powder in said reservoir wherein said powder comprises a        plurality of perforated microstructures having a bulk density of        less than about 0.5 g/cm³ wherein said perforated microstructure        powder comprises a bioactive agent whereby said inhalation        device provides for the aerosolized administration of said        powder to at least a portion of the pulmonary air passages of a        patient in need thereof. As alluded to above, it will be        appreciated that an inhalation device may comprise an atomizer,        a sprayer, a dry powder inhaler, a metered dose inhaler or a        nebulizer. Moreover, the reservoir may be a unit dose container        or bulk reservior.

In other embodiments, the perforated microstructure powders may bedispersed in an appropriate suspension medium to provide stabilizeddispersions for delivery of a selected agent. Such dispersions areparticularly useful in metered dose inhalers and nebulizers. In thisregard, particularly preferred suspension mediums comprisefluorochemicals (e.g. perfluorocarbons or fluorocarbons) that are liquidat room temperature. As discussed above, It is well established thatmany fluorochemicals have a proven history of safety andbiocompatibility in the lung. Further, in contrast to aqueous solutions,fluorochemicals do not negatively impact gas exchange. Moreover, becauseof their unique wettability characteristics, fluorochemicals may be ableto provide for the dispersion of particles deeper into the lung, therebyimproving systemic delivery. Finally, many fluorochemicals are alsobacteriostatic thereby decreasing the potential for microbial growth incompatible preparations.

Whether administered in the form of a dry powder or stabilizeddispersion, the present invention provides for the effective delivery ofbioactive agents. As used herein, the terms “bioactive agent” refers toa substance which is used in connection with an application that istherapeutic or diagnostic in nature, such as methods for diagnosing thepresence or absence of a disease in a patient and/or methods fortreating disease in a patient. As to compatible bioactive agents, thoseskilled in the art will appreciate that any therapeutic or diagnosticagent may be incorporated in the stabilized dispersions of the presentinvention. For example, the bioactive agent may be selected from thegroup consisting of antiallergics, bronchodilators, bronchoconstrictors,pulmonary lung surfactants, analgesics, antibiotics, leukotrieneinhibitors or antagonists, anticholinergics, mast cell inhibitors,antihistamines, antiinflammatories, antineoplastics, anesthetics,anti-tuberculars, imaging agents, cardiovascular agents, enzymes,steroids, genetic material, viral vectors, antisense agents, proteins,peptides and combinations thereof In preferred embodiments the bioactiveagents comprise compounds which are to be administered systemically(i.e. to the systemic circulation of a patient) such as peptides,proteins or polynucleotides. As will be disclosed in more detail below,the bioactive agent may be incorporated, blended in, coated on orotherwise associated with the perforated microstructure.

Accordingly, the present invention provides methods for the pulmonarydelivery of one or more bioactive agents comprising the steps of:

-   -   providing a powder comprising a plurality of perforated        microstructures having a bulk density of less than about 0.5        g/cm³ wherein said perforated microstructure powder comprises a        bioactive agent;    -   aerosolizing said perforated microstructure powder to provide an        aerosolized medicament; and    -   administering a therapeutically effective amount of said        aerosolized medicament to at least a portion of the nasal or        pulmonary passages of a patient in need thereof.

As used herein the term “aerosolized” shall be held to mean a gaseoussuspension of fine solid or liquid particles unless otherwise dictatedby contextual restraints. That is, an aerosol or aerosolized medicamentmay be generated, for example, by a dry powder inhaler, a metered doseinhaler, an atomizer or a nebulizer.

With respect to the disclosed powders, the selected agent or bioactiveagent, or agents, may be used as the sole structural component of theperforated microstructures. Conversely, the perforated microstructuresmay comprise one or more components (i.e. structural materials,surfactants, excipients, etc.) in addition to the incorporated agent. Inparticularly preferred embodiments, the suspended perforatedmicrostructures will comprise relatively high concentrations ofsurfactant (greater than about 10% w/w) along with an incorporatedbioactive agent(s). Finally, it should be appreciated that theparticulate or perforated microstructure may be coated, linked orotherwise associated with an agent or bioactive agent in a non-integralmanner. Whatever configuration is selected, it will be appreciated thatany associated bioactive agent may be used in its natural form, or asone or more salts known in the art.

While the powders or stabilized dispersions of the present invention areparticularly suitable for the pulmonary administration of bioactiveagents, they may also be used for the localized or systemicadministration of compounds to any location of the body. Accordingly, itshould be emphasized that, in preferred embodiments, the formulationsmay be administered using a number of different routes including, butnot limited to, the gastrointestinal tract, the respiratory tract,topically, intramuscularly, intraperitoneally, nasally, vaginally,rectally, aurally, orally or ocularly.

Other objects, features and advantages of the present invention will beapparent to those skilled in the art from a consideration of thefollowing detailed description of preferred exemplary embodimentsthereof.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A1 to 1F2 illustrate changes in particle morphology as a functionof variation in the ratio of fluorocarbon blowing agent to phospholipid(PFC/PC) present in the spray dry feed. The micrographs, produced usingscanning electron microscopy and transmission electron microscopytechniques, show that in the absence of FCs, or at low PFC/PC ratios,the resulting spray dried microstructures comprising gentamicin sulfateare neither particularly hollow nor porous. Conversely, at high PFC/PCratios, the particles contain numerous pores and are substantiallyhollow with thin walls.

FIG. 2 depicts the suspension stability of gentamicin particles inPerflubron as a function of formulation PFC/PC ratio or particleporosity. The particle porosity increased with increasing PFC/PC ratio.Maximum stability was observed with PFC/PC ratios between 3 to 15,illustrating a preferred morphology for the perflubron suspension media.

FIG. 3 is a scanning electron microscopy image of perforatedmicrostructures comprising cromolyn sodium illustrating a preferredhollow/porous morphology.

FIGS. 4A to 4D are photographs illustrating the enhanced stabilityprovided by the dispersions of the present invention over time ascompared to a commercial cromolyn sodium formulation (Intal®,Rhone-Poulenc-Rorer). In the photographs, the commercial formulation onthe left rapidly separates while the dispersion on the right, formed inaccordance with the teachings herein, remains stable over an extendedperiod.

FIG. 5 presents results of in-vitro Andersen cascade impactor studiescomparing the same hollow porous albuterol sulfate formulation deliveredvia a MDI in HFA-134a, or from an exemplary DPI. Efficient delivery ofparticles was observed from both devices. MDI delivery of the particleswas maximized on plate 4 corresponding to upper airway delivery. DPIdelivery of the particles results in substantial deposition on the laterstages in the impacts corresponding to improved systemic deliveryin-vivo.

DETAILED DESCRIPTION PREFERRED EMBODIMENTS

While the present invention may be embodied in many different forms,disclosed herein are specific illustrative embodiments thereof thatexemplify the principles of the invention. It should be emphasized thatthe present invention is not limited to the specific embodimentsillustrated.

As discussed above, the present invention provides methods, systems andcompositions that comprise perforated microstructures which, inpreferred embodiments, may advantageously be used for the delivery ofbioactive agents. In particularly preferred embodiments, the disclosedperforated microstructure powders may be used in a dry state (e.g. as ina DPI) or in the form of a stabilized dispersion (e.g. as in a MDI, LDIor nebulizer formulation) to deliver bioactive agents to the nasal orpulmonary air passages of a patient. It will be appreciated that theperforated microstructures disclosed herein comprise a structural matrixthat exhibits, defines or comprises voids, pores, defects, hollows,spaces, interstitial spaces, apertures, perforations or holes. Theabsolute shape (as opposed to the morphology) of the perforatedmicrostructure is generally not critical and any overall configurationthat provides the desired characteristics is contemplated as beingwithin the scope of the invention. Accordingly, preferred embodimentscan comprise approximately microspherical shapes. However, collapsed,deformed or fractured particulates are also compatible. With thiscaveat, it will further be appreciated that, particularly preferredembodiments of the invention comprise spray dried hollow, porousmicrospheres. In any case the disclosed powders of perforatedmicrostructures provide several advantages including, but not limitedto, increases in suspension stability, improved dispersibility, superiorsampling characteristics, elimination of carrier particles and enhancedaerodynamics.

Those skilled in the art will appreciate that many of these aspects areof particular use for dry powder inhaler applications. Unlike prior artformulations, the present invention provides unique methods andcompositions to reduce cohesive forces between dry particles, thereby,minimizing particulate aggregation which can result in an improveddelivery efficiency. As such, the disclosed preparations provide ahighly flowable, dry powders that can be efficiently aerosolized,uniformly delivered and penetrate deeply in the lung or nasal passages.Furthermore, the perforated microstructures of the present inventionresult in surprisingly low throat deposition upon administration.

In preferred embodiments, the perforated microstructure powders haverelatively low bulk density, allowing the powders to provide superiorsampling properties over compositions known in the art. Currently, asexplained above, many commercial dry powder formulations comprise largelactose particles which have micronized drug aggregated on theirsurface. For these prior art formulations, the lactose particles serveas a carrier for the active agents and as a bulking agent, therebyproviding means to partially control the fine particle dose deliveredfrom the device. In addition, the lactose particles provide the meansfor the commercial filling capability of dry particles into unit dosecontainers by adding mass and volume to the dosage form.

By way of contrast, the present invention uses methods and compositionsthat yield powder formulations having extraordinarily low bulk density,thereby reducing the minimal filling weight that is commerciallyfeasible for use in dry powder inhalation devices. That is, most unitdose containers designed for DPIs are filled using fixed volume orgravimetric techniques. Contrary to prior art formulations, the presentinvention provides powders wherein the active or bioactive agent and theincipients or bulking agents make-up the entire inhaled particle.Compositions according to the present invention typically yield powderswith bulk densities less than 0.5 g/cm³ or 0.3 g/cm³, preferably less0.1 g/cm³ and most preferably less than 0.05 g/cm³. By providingparticles with very low bulk density, the minimum powder mass that canbe filled into a unit dose container is reduced, which eliminates theneed for carrier particles. That is, the relatively low density of thepowders of the present invention provides for the reproducibleadministration of relatively low dose pharmaceutical compounds.Moreover, the elimination of carrier particles will potentially minimizethroat deposition and any “gag” effect, since the large lactoseparticles will impact the throat and upper airways due to their size.

In accordance with the teachings herein the perforated microstructureswill preferably be provided in a “dry” state. That is the microparticleswill possess a moisture content that allows the powder to remainchemically and physically stable during storage at ambient temperatureand easily dispersible. As such, the moisture content of themicroparticles is typically less than 6% by weight, and preferably less3% by weight. In some instances the moisture content will be as low as1% by weight. Of course it will be appreciated that the moisture contentis, at least in part, dictated by the formulation and is controlled bythe process conditions employed, e.g., inlet temperature, feedconcentration, pump rate, and blowing agent type, concentration and postdrying.

With respect to the composition of the structural matrix defining theperforated microstructures, they may be formed of any material whichpossesses physical and chemical characteristics that are compatible withany incorporated active agents. While a wide variety of materials may beused to form the particles, in particularly preferred pharmaceuticalembodiments the structural matrix is associated with, or comprises, asurfactant such as phospholipid or fluorinated surfactant. Although notrequired, the incorporation of a compatible surfactant can improvepowder flowability, increase aerosol efficiency, improve dispersionstability, and facilitate preparation of a suspension. It will beappreciated that, as used herein, the terms “structural matrix” or“microstructure matrix” are equivalent and shall be held to mean anysolid, material forming the perforated microstructures which define aplurality of voids, apertures, hollows, defects, pores, holes, fissures,etc. that provide the desired characteristics. In preferred embodiments,the perforated microstructure defined by the structural matrix comprisesa spray dried hollow porous microsphere incorporating at least onesurfactant. It will further be appreciated that, by altering the matrixcomponents, the density of the structural matrix may be adjusted.Finally, as will be discussed in further detail below, the perforatedmicrostructures preferably comprise at least one active or bioactiveagent.

As indicated, the perforated microstructures of the present inventionmay optionally be associated with, or compose, one or more surfactants.Moreover, miscible surfactants may optionally be combined in the casewhere the microparticles are formulated in a suspension medium liquidphase. It will be appreciated by those skilled in the art that the useof surfactants, while not necessary to practice the instant invention,may further increase dispersion stability, powder flowability, simplifyformulation procedures or increase efficiency of delivery. Of coursecombinations of surfactants, including the use of one or more in theliquid phase and one or more associated with the perforatedmicrostructures are contemplated as being within the scope of theinvention. By “associated with or comprise” it is meant that thestructural matrix or perforated microstructure may incorporate, adsorb,absorb, be coated with or be formed by the surfactant.

In a broad sense, surfactants suitable for use in the present inventioninclude any compound or composition that aids in the formation ofperforated microparticles or provides enhanced suspension stability,improved powder dispersibility or decreased particle aggregation. Thesurfactant may comprise a single compound or any combination ofcompounds, such as in the case of co-surfactants. Particularly preferredsurfactants are nonfluorinated and selected from the group consisting ofsaturated and unsaturated lipids, nonionic detergents, nonionic blockcopolymers, ionic surfactants and combinations thereof. In thoseembodiments comprising stabilized dispersions, such nonfluorinatedsurfactants will preferably be relatively insoluble in the suspensionmedium. It should be emphasized that, in addition to the aforementionedsurfactants, suitable fluorinated surfactants are compatible with theteachings herein and may be used to provide the desired preparations.

Lipids, including phospholipids, from both natural and synthetic sourcesare particularly compatible with the present invention and may be usedin varying concentrations to form the structural matrix. Generallycompatible lipids comprise those that have a gel to liquid crystal phasetransition greater than about 40° C. Preferably the incorporated lipidsare relatively long chain (i.e. C₁₆-C₂₂) saturated lipids and morepreferably comprise phospholipids. Exemplary phospholipids useful in thedisclosed stabilized preparations comprise,dipalmitoylphosphatidylcholine, disteroylphosphatidylcholine,diarachidoylphosphatidylcholine dibehenoylphosphatidylcholine,short-chain phosphatidylcholines, long-chain saturatedphosphatidylethanolamines, long-chain saturated phosphatidylserines,long-chain saturated phosphatidylglycerols, long-chain saturatedphosphatidylinositols, glycolipids, ganglioside GMI, sphingomyelin,phosphatidic acid, cardiolipin; lipids bearing polymer chains such aspolyethylene glycol, chitin, hyaluronic acid, or polyvinylpyrrolidone;lipids bearing sulfonated mono-, di-, and polysaccharides; fatty acidssuch as palmitic acid, stearic acid, and oleic acid; cholesterol,cholesterol esters, and cholesterol hemisuccinate. Due to theirexcellent biocompatibility characteristics, phospholipids andcombinations of phospholipids and poloxamers are particularly suitablefor use in the pharmaceutical embodiments disclosed herein.

Compatible nonionic detergents comprise: sorbitan esters includingsorbitan trioleate (Span® 85), sorbitan sesquioleate, sorbitanmonooleate, sorbitan monolaurate, polyoxyethylene (20) sorbitanmonolaurate, and polyoxyethylene (20) sorbitan monooleate, oleylpolyoxyethylene (2) ether, stearyl polyoxyethylene (2) ether, laurylpolyoxyethylene (4) ether, glycerol esters, and sucrose esters. Othersuitable nonionic detergents can be easily identified using McCutcheon'sEmulsifiers and Detergents (McPublishing Co., Glen Rock, N.J.) which isincorporated herein in its entirety. Preferred block copolymers includediblock and triblock copolymers of polyoxyethylene and polyoxypropylene,including poloxamer 188 (Pluronic® F-68), poloxamer 407 (Pluronic®F-127), and poloxamer 338. Ionic surfactants such as sodiumsulfosuccinate, and fatty acid soaps may also be utilized. In preferredembodiments the microstructures may comprise oleic acid or its alkalisalt.

In addition to the aforementioned surfactants, cationic surfactants orlipids are preferred especially in the case of delivery or RNA or DNA.Examples of suitable cationic lipids include: DOTMA,N-[1-(2,3-dioleyloxy)propyl]-N,N,N-trimethylammonium chloride; DOTAP,1,2-dioleyloxy-3-(trimethylammonio)propane;. and DOTB,1,2-dioleyl-3-(4′-trimethylammonio)butanoyl-sn-glycerol. Polycationicamino acids such as polylysine, and polyarginine are also contemplated.

Besides those surfactants enumerated above, it will further beappreciated that a wide range of surfactants may optionally be used inconjunction with the present invention. Moreover, the optimum surfactantor combination thereof for a given application can readily be determinedby empirical studies that do not require undue experimentation. Finally,as discussed in more detail below, surfactants comprising the structuralmatrix may also be useful in the formation of precursor oil-in-wateremulsions (i.e. spray drying feed stock) used during processing to formthe perforated microstructures.

Unlike prior art formulations, it has surprisingly been found that theincorporation of relatively high levels of surfactants (e.g.,phospholipids) may be used to improve powder dispersibility, increasesuspension stability and decrease powder aggregation of the disclosedapplications. That is, on a weight to weight basis, the structuralmatrix of the perforated microstructures may comprise relatively highlevels of surfactant. In this regard, the perforated microstructureswill preferably comprise greater than about 1%, 5%, 10%, 15%, 18%, oreven 20% w/w surfactant. More preferably, the perforated microstructureswill comprise greater than about 25%, 30%, 35%, 40%, 45%, or 50% w/wsurfactant. Still other exemplary embodiments will comprise perforatedmicrostructures wherein the surfactant or surfactants are present atgreater than about 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90% or even 95%w/w. In selected embodiments the perforated microstructures willcomprise essentially 100% w/w of a surfactant such as a phospholipid.Those skilled in the art will appreciate that, in such cases, thebalance of the structural matrix (where applicable) will likely comprisea bioactive agent or non surface active excipients or additives.

While such surfactant levels are preferably employed in perforatedmicrostructures, they may be used to provide stabilized systemscomprising relatively nonporous, or substantially solid, particulates.That is, while preferred embodiments will comprise perforatedmicrostructures associated with high levels of surfactant, acceptablemicrospheres may be formed using relatively low porosity particulates ofthe same surfactant concentration (i.e. greater than about 20% w/w). Inthis respect such high surfactarit embodiments are specificallycontemplated as being within the scope of the present invention.

In other preferred embodiments, of the invention the structural matrixdefining the perforated microstructure optionally comprises synthetic ornatural polymers or combinations thereof. In this respect usefulpolymers comprise polylactides,. polylactide-glycolides, cyclodextrins,polyacrylates, methylcellulose, carboxymethylcellulose, polyvinylalcohols, polyanhydrides, polylactams, polyvinyl pyrrolidones,polysaccharides (dextrans, starches, chitin, chitosan, etc.), hyaluronicacid, proteins, (albumin, collagen, gelatin, etc.). Examples ofpolymeric resins that would be useful for the preparation of perforatedink microparticles include: styrene-butadiene, styrene-isoprene,styrene-acrylonitrile, ethylene-vinyl acetate, ethylene-acrylate,ethylene-acrylic acid, ethylene-methylacrylate, ethylene-ethyl acrylate,vinyl-methyl methacrylate, acrylic acid-methyl methacrylate, and vinylchloride-vinyl acetate. Those skilled in the art will appreciate that,by selecting the appropriate polymers, the delivery efficiency of theperforated microparticles and/or the stability of the dispersions may betailored to optimize the effectiveness of the active or bioactive agent.

Besides the aforementioned polymer materials and surfactants, it may bedesirable to add other excipients to a microsphere formulation toimprove particle rigidity, production yield, delivery efficiency anddeposition, shelf-life and patient acceptance. Such optional excipientsinclude, but are not limited to: coloring agents, taste masking agents,buffers, hygroscopic agents, antioxidants, and chemical stabilizers.Further, various excipients may be incorporated in, or added to, theparticulate matrix to provide structure and form to the perforatedmicrostructures (i.e. microspheres such as latex particles). In thisregard it will be appreciated that the rigidifying components can beremoved using a post-production technique such as selective solventextraction.

Other rigidifying excipients may include but are not limited to,carbohydrates including monosaccharides, disaccharides andpolysaccharides. For example, monosaccharides such as dextrose(anhydrous and monohydrate), galactose, mannitol, D-mannose, sorbitol,sorbose and the like; disaccharides such as lactose, maltose, sucrose,trehalose, and the like; trisaccharides such as raffinose and the like;and other carbohydrates such as starches (hydroxyethylstarch),cyclodextrins and maltodextrins. Amino acids are also suitableexcipients with glycine preferred. Mixtures of carbohydrates and aminoacids are further held to be within the scope of the present invention.The inclusion of both inorganic (e.g. sodium chloride, calcium chloride,etc.), organic salts (e.g. sodium citrate, sodium ascorbate, magnesiumgluconate, sodium gluconate, tromethamine hydrochloride, etc.) andbuffers is also contemplated. The inclusion of salts and organic solidssuch as ammonium carbonate, ammonium acetate, ammonium chloride orcamphor are also contemplated.

Yet other preferred embodiments include perforated microstructures thatmay comprise, or may be coated with, charged species that prolongresidence time at the point of contact or enhance penetration throughmucosae. For example, anionic charges are known to favor mucoadhesionwhile cationic charges may be used to associate the formedmicroparticulate with negatively charged bioactive agents such asgenetic material. The charges may be imparted through the association orincorporation of polyanionic or polycationic materials such aspolyacrylic acids, polylysine, polylactic acid and chitosan.

In addition to, or instead of, the components discussed above, theperforated microstructures will preferably comprise at least one activeor bioactive agent. As used herein, the term “active agent” simplyrefers to a substance that enables the perforated microstructures toperform the desired function. Further, the term “active agent” shall beheld inclusive of the term “bioactive agent” unless otherwise dictatedby contextual restraints. As to the term “bioactive agent” it shall beheld to comprise any substance that is used in connection with thediagnosis or treatment of a disease, condition or physiologicalabnormality in a patient. Particularly preferred bioactive agents foruse in accordance with the invention include anti-allergics, peptidesand proteins, pulmonary lung surfactants, bronchodilators andanti-inflammatory steroids for use in the treatment of respiratorydisorders such as asthma by inhalation therapy. Preferred active agentsfor use in accordance with the present invention include pigments, dyes,inks, paints, detergents, food sweeteners, spices, adsorbants,absorbents, catalysts, nucleating agents, thickening agents, polymers,resins, insulators, fillers, fertilizers, phytohormones, insectpheromones, insect repellents, pet repellents, antifouling agents,pesticides, fungicides, disinfectants, perfumes, deodorants, andcombinations of thereof.

It will be appreciated that the perforated microstructures of thepresent invention may exclusively comprise one or more active orbioactive agents (i.e. 100% w/w). However, in selected embodiments theperforated microstructures may incorporate much less bioactive agentdepending on the activity thereof. Accordingly, for highly activematerials the perforated microstructures may incorporate as little as0.001% by weight although a concentration of greater than about 0.1% w/wis preferred. Other embodiments of the invention may comprise greaterthan about 5%, 10%, 15%, 20%, 25%, 30% or even 40% w/w active orbioactive agent. Still more preferably the perforated microstructuresmay comprise greater than about 50%, 60%, 70%, 75%, 80% or even 90% wIwactive or bioactive agent. The precise amount of active or bioactiveagent incorporated in the perforated microstructures of the presentinvention is dependent upon the agent of choice, the required dose, andthe form of the agent actually used for incorporation. Those skilled inthe art will appreciate that such determinations may be made by usingwell-known pharmacological techniques in combination with the teachingsof the present invention.

With regard to pharmaceutical preparations, any bioactive agent that maybe formulated in the disclosed perforated microstructures is expresslyheld to be within the scope of the present invention. In particularlypreferred embodiments, the selected bioactive agent may be administeredin the form of an aerosolized medicaments. Accordingly, particularlycompatible bioactive agents comprise any drug that may be formulated asa flowable dry powder or which is relatively insoluble in selecteddispersion media. In addition, it is preferred that the formulatedagents are subject to pulmonary or nasal uptake in physiologicallyeffective amounts. Compatible bioactive agents comprise hydrophilic andlipophilic respiratory agents, pulmonary surfactants, bronchodilators,antibiotics, antivirals, anti-inflammatories, steroids, antihistaminics,leukotriene inhibitors or antagonists, anticholinergics,antineoplastics, anesthetics, enzymes, cardiovascular agents, geneticmaterial including DNA and RNA, viral vectors, immunoactive agents,imaging agents, vaccines, immunosuppressive agents, peptides, proteinsand combinations thereof. Particularly preferred bioactive agents forinhalation therapy comprise mast cell inhibitors (anti-allergics),bronchodilators, and anti-inflammatory steroids such as, for example,cromoglycate (e.g. the sodium salt), and albuterol (e.g. the sulfatesalt).

More specifically, exemplary medicaments or bioactive agents may beselected from, for example, analgesics, e.g. codeine, dihydromorphine,ergotamine, fentanyl, or morphine; anginal preparations, e.g. diltiazem;mast cell inhibitors, e.g. cromolyn sodium; antiinfectives, e.g.cephalosporins, macrolides, quinolines, penicillins, streptomycin,sulphonamides, tetracyclines and pentamidine; antihistamines, e.g.methapyrilene; anti-inflammatories, e.g. fluticasone propionate,beclomethasone dipropionate, flunisolide, budesonide, tripedane,cortisone, prednisone, prednisilone, dexamethasone, betamethasone, ortriamcinolone acetonide; antitussives, e.g. noscapine; bronchodilators,e.g. ephedrine, adrenaline, fenoterol, formoterol, isoprenaline,metaproterenol, salbutamol, albuterol, salmeterol, terbutaline;diuretics, e.g. amiloride; anticholinergics, e.g. ipatropium, atropine,or okitropium; lung surfactants e.g. Surfaxin, Exosurf, Survanta;xanthines, e.g. aminophylline, theophylline, caffeine; therapeuticproteins and peptides, e.g. DNAse, insulin, glucagon, LHRH, nafarelin,goserelin, leuprolide, interferon, rhu IL-1 receptor, macrophageactivation factors such as lymphokines and muramyl dipeptides, opioidpeptides and neuropeptides such as enkaphalins, endophins, renininhibitors, cholecystokinins, DNAse, growth hormones, leukotrieneinhibitors and the like. In addition, bioactive agents that comprise anRNA or DNA sequence, particularly those useful for gene therapy, geneticvaccination, genetic tolerization or antisense applications, may beincorporated in the disclosed dispersions as described herein.Representative DNA plasmids include, but are not limited to pCMVβ(available from Genzyme Corp, Framington, Mass.) and pCMV-β-gal (a CMVpromotor linked to the E. coli Lac-Z gene, which codes for the enzymeβ-galactosidase).

In any event, the selected active or bioactive agent(s) may beassociated with, or incorporated in, the perforated microstructures inany form that provides the desired efficacy and is compatible with thechosen production techniques. As used herein, the terms “associate” or“associating” mean that the structural matrix or perforatedmicrostructure may comprise, incorporate, adsorb, absorb, be coated withor be formed by the active or bioactive agent. Where appropriate, theactives may be used in the form of salts (e.g. alkali metal or aminesalts or as acid addition salts) or as esters or as solvates (hydrates).In this regard the form of the active or bioactive agents may beselected to optimize the activity and/or stability of the actives and/orto minimize the solubility of the agent in the suspension medium and/orto minimize particle aggregation.

It will further be appreciated that the perforated microstructuresaccording to the invention may, if desired, contain a combination of twoor more active ingredients. The agents may be provided in combination ina single species of perforated microstructure or individually inseparate species of perforated microstructures. For example, two or moreactive or bioactive agents may be incorporated in a single feed stockpreparation and spray dried to provide a single microstructure speciescomprising a plurality of active agents. Conversely, the individualactives could be added to separate stocks and spray dried separately toprovide a plurality of microstructure species with differentcompositions. These individual species could be added to the suspensionmedium or dry powder dispensing compartment in any desired proportionand placed in the aerosol delivery system as described below. Further,as alluded to above, the perforated microstructures (with or without anassociated agent) may be combined with one or more conventional (e.g. amicronized drug) active or bioactive agents to provide the desireddispersion stability or powder dispersibility.

Based on the foregoing, it will be appreciated by those skilled in theart that a wide variety of active or bioactive agents may beincorporated in the disclosed perforated microstructures. Accordingly,the list of preferred active agents above is exemplary only and notintended to be limiting. It will also be appreciated by those skilled inthe art that the proper amount of bioactive agent and the timing of thedosages may be determined for the formulations in accordance withalready existing information and without undue experimentation.

As seen from the passages above, various components may be associatedwith, or incorporated in the perforated microstructures of the presentinvention. Similarly, several techniques may be used to provideparticulates having the desired morphology (e.g. a perforated orhollow/porous configuration), dispersibility and density. Among othermethods, perforated microstructures compatible with the instantinvention may be formed by techniques including spray drying, vacuumdrying, solvent extraction, emulsification or lyophilization, andcombinations thereof. It will further be appreciated that the basicconcepts of many of these techniques are well known in the prior art andwould not, in view of the teachings herein, require undueexperimentation to adapt them so as to provide the desired perforatedmicrostructures.

While several procedures are generally compatible with the presentinvention, particularly preferred embodiments typically compriseperforated microstructures formed by spray drying. As is well known,spray drying is a one-step process that converts a liquid feed to adried particulate form. With respect to pharmaceutical applications, itwill be appreciated that spray drying has been used to provide powderedmaterial for various administrative routes including inhalation. See,for example, M. Sacchetti and M. M. Van Oort in: Inhalation Aerosols:Physical and Biological Basis for Therapy, A. J. Hickey, ed. MarcelDekkar, New York, 1996, which is incorporated herein by reference.

In general, spray drying consists of bringing together a highlydispersed liquid, and a sufficient volume of hot air to produceevaporation and drying of the liquid droplets. The preparation to bespray dried or feed (or feed stock) can be any solution, coursesuspension, slurry, colloidal dispersion, or paste that may be atomizedusing the selected spray drying apparatus. In preferred embodiments thefeed stock will comprise a colloidal system such as an emulsion, reverseemulsion, microemulsion, multiple emulsion, particulate dispersion, orslurry. Typically the feed is sprayed into a current of warm filteredair that evaporates the solvent and conveys the dried product to acollector. The spent air is then exhausted with the solvent. Thoseskilled in the art will appreciate that several different types ofapparatus may be used to provide the desired product. For example,commercial spray dryers manufactured by Buchi Ltd. or Niro Corp. willeffectively produce particles of desired size.

It will further be appreciated that these spray dryers, and specificallytheir atomizers, may be modified or customized for specializedapplications, i.e. the simultaneous spraying of two solutions using adouble nozzle technique. More specifically, a water-in-oil emulsion canbe atomized from one nozzle and a solution containing an anti-adherentsuch as mannitol can be co-atomized from a second nozzle. In other casesit may be desirable to push the feed solution though a custom designednozzle using a high pressure liquid chromatography (HPLC) pump. Providedthat microstructures comprising the correct morphology and/orcomposition are produced the choice of apparatus is not critical andwould be apparent to the skilled artisan in view of the teachings,herein.

While the resulting spray-dried powdered particles typically areapproximately spherical in shape, nearly uniform in size and frequentlyare hollow, there may be some degree of irregularity in shape dependingupon the incorporated medicament and the spray drying conditions. Inmany instances dispersion stability and dispersibility of the perforatedmicrostructures appears to be improved if an inflating agent (or blowingagent) is used in their production. Particularly preferred embodimentsmay comprise an emulsion with the inflating agent as the disperse orcontinuous phase. The inflating agent is preferably dispersed with asurfactant solution, using, for instance, a commercially availablemicrofluidizer at a pressure of about 5000 to 15,000 psi. This processforms an emulsion, preferably stabilized by an incorporated surfactant,typically comprising submicron droplets of water immiscible blowingagent dispersed in an aqueous continuous phase. The formation of suchemulsions using this and other techniques are common and well known tothose in the art. The blowing agent is preferably a fluorinated compound(e.g. perfluorohexane, perfluorooctyl bromide, perfluorodecalin,perfluorobutyl ethane) which vaporizes during the spray-drying process,leaving behind generally hollow, porous aerodynamically lightmicrospheres. As will be discussed in more detail below, other suitableliquid blowing agents include nonfluorinated oils, chloroform, Freons,ethyl acetate, alcohols and hydrocarbons. Nitrogen and carbon dioxidegases are also contemplated as a suitable blowing agent.

Besides the aforementioned compounds, inorganic and organic substanceswhich can be removed under reduced pressure by sublimation in apost-production step are also compatible with the instant invention.These sublimating compounds can be dissolved or dispersed as micronizedcrystals in the spray drying feed solution and include ammoniumcarbonate and camphor. Other compounds compatible with the presentinvention comprise rigidifying solid structures which can be dispersedin the feed solution or prepared in-situ. These structures are thenextracted after the initial particle generation using a post-productionsolvent extraction step. For example, latex particles can be dispersedand subsequently dried with other wall forming compounds, followed byextraction with a suitable solvent.

Although the perforated microstructures are preferably formed using ablowing agent as described above, it will be appreciated that, in someinstances, no additional blowing agent is required and ail aqueousdispersion of the medicament and/or excipients and surfactant(s) arespray dried directly. In such cases, the formulation may be amenable toprocess conditions (e.g., elevated temperatures) that may lead to theformation of hollow, relatively porous microparticles. Moreover, themedicament may possess special physicochemical properties (e.g., highcrystallinity, elevated melting temperature, surface activity, etc.)that makes it particularly suitable for use in such techniques.

When a blowing agent is employed, the degree of porosity anddispersibility of the perforated microstructure appears to depend, atleast in part, on the nature of the blowing agent, its concentration inthe feed stock (e.g. as an emulsion), and the spray drying conditions.With respect to controlling porosity and, in suspensions, dispersibilityit has surprisingly been found that the use of compounds, heretoforeunappreciated as blowing agents, may provide perforated microstructureshaving particularly desirable characteristics. More particularly, inthis novel and unexpected aspect of the present invention it has beenfound that the use of fluorinated compounds having relatively highboiling points (i.e. greater than about 40° C.) may be used to produceparticulates that are particularly porous. Such perforatedmicrostructures are especially suitable for inhalation therapies. Inthis regard it is possible to use fluorinated or partially fluorinatedblowing agents having boiling points of greater than about 40° C., 50°C., 60° C., 70° C., 80° C., 90° C. or even 95° C. Particularly preferredblowing agents have boiling points greater than the boiling point ofwater, i.e. greater than 100° C. (e.g. perflubron, perfluorodecalin). Inaddition blowing agents with relatively low water solubility (<10⁻⁶ M)are preferred since they enable the production of stable emulsiondispersions with mean weighted particle diameters less than 0.3 μm.

As previously described, these blowing agents will preferably beincorporated in an emulsified feed stock prior to spray drying. For thepurposes of the present invention this feed stock will also preferablycomprise one or more active or bioactive agents, one or more surfactantsor one or more excipients. Of course, combinations of the aforementionedcomponents are also within the scope of the invention. While highboiling (>100° C.) fluorinated blowing agents comprise one preferredaspect of the present invention, it will be appreciated-thatnonfluorinated blowing agents with similar boiling points (>100° C.) maybe used to provide perforated microstructures. Exemplary nonfluorinatedblowing agents suitable for use in the present invention comprise theformula:R¹—X—R² or R¹—Xwherein: R¹ or R² is hydrogen, alkyl, alkenyl, alkynyl, aromatic, cyclicor combinations thereof, X is any group containing carbon, sulfur,nitrogen, halogens, phosphorus, oxygen and combinations thereof.

While not limiting the invention in any way it is hypothesized that, asthe aqueous feed component evaporates during spray drying it leaves athin crust at the surface of the particle. The resulting particle wallor crust formed during the initial moments of spray drying appears totrap any high boiling blowing agents as hundreds of emulsion droplets(ca. 200-300 nm). As the drying process continues, the pressure insidethe particulate increases thereby vaporizing at least part of theincorporated blowing agent and forcing it through the relatively thincrust. This venting or outgassing apparently leads to the formation ofpores or other defects in the microstructure. At the same time remainingparticulate components (possibly including some blowing agent) migratefrom the interior to the surface as the particle solidifies. Thismigration apparently slows during the drying process as a result ofincreased resistance to mass transfer caused by an increased internalviscosity. Once the migration ceases the particle solidifies, leavingvoids, pores, defects, hollows, spaces, interstitial spaces, apertures,perforations or holes. The number of pores or defects, their size, andthe resulting wall thickness is largely dependent on the formulationand/or the nature of the selected blowing agent (e.g. boiling point),its concentration in the emulsion, total solids concentration, and thespray-drying conditions. It can be greatly appreciated that this type ofparticle morphology in part contributes to the improved powderdispersibility, suspension stability and aerodynamics.

It has been surprisingly found that substantial amounts of theserelatively high boiling blowing agents may be retained in the resultingspray dried product. That is, spray dried perforated microstructures asdescribed herein may comprise as much as 1%, 3%, 5%, 10%, 20%, 30% oreven 40% w/w of the blowing agent. In such cases, higher productionyields were obtained as a result an increased particle density caused byresidual blowing agent. It will be appreciated by those skilled in theart that retained fluorinated blowing agent may alter the surfacecharacteristics of the perforated microstructures, thereby minimizingparticle aggregation during processing and further increasing dispersionstability. Residual fluorinated blowing agent in the particle may alsoreduce the cohesive forces between particles by providing a barrier orby attenuating the attractive forces produced during manufacturing(e.g., electrostatics). This reduction in cohesive forces may beparticularly advantageous when using the disclosed microstructures inconjunction with dry powder inhalers.

Furthermore, the amount of residual blowing agent can be attenuatedthrough the process conditions (such as outlet temperature), blowingagent concentration, or boiling point. If the outlet temperature is ator above the boiling point, the blowing agent escapes the particle andthe production yield decreases. Preferred outlet temperature willgenerally be operated at 20, 30, 40, 50, 60, 70, 80, 90 or even 100° C.less than the blowing agent boiling point. More preferably thetemperature differential between the outlet temperature and the boilingpoint will range from 50 to 150° C. It will be appreciated by thoseskilled in the art that particle porosity, production yield,electrostatics and dispersibility can be optimized by first identifyingthe range of process conditions (e.g., outlet temperature) that aresuitable for the selected active agents and/or excipients. The preferredblowing agent can be then chosen using the maximum outlet temperaturesuch that the temperature differential with be at least 20 and up to150° C. In some cases, the temperature differential can be outside thisrange such as, for example, when producing the particulates undersupercritical conditions or using lyophilization techniques. Thoseskilled in the art will further appreciate that the preferredconcentration of blowing agent can be determined experimentally withoutundue experimentation using techniques similar to those described in theExamples herein.

While residual blowing agent may be advantageous in selected embodimentsit may be desirable to substantially remove any blowing agent from thespray dried product. In this respect, the residual blowing agent caneasily be removed with a post-production evaporation step in a vacuumoven. Moreover, such post production techniques may be used to provideperforations in the particulates. For example, pores may be formed byspray drying a bioactive agent and an excipient that can be removed fromthe formed particulates under a vacuum.

In any event, typical concentrations of blowing agent in the feed stockare between 2% and 50% v/v, and more preferably between about 10% to 45%v/v. In other embodiments blowing agent concentrations will preferablybe greater than about 5%, 10%, 15%, 20%, 25% or even 30% v/v. Yet otherfeed stock emulsions may comprise 35%, 40%, 45% or even 50% v/v of theselected high boiling point compound.

In preferred embodiments, another method of identifying theconcentration of blowing agent used in the feed is to provide it as aratio of the concentration of the blowing agent to that of thestabilizing surfactant (e.g. phosphatidylcholine or PC) in the precursoror feed emulsion. For fluorocarbon blowing agents (e.g. perfluorooctylbromide), and for the purposes of explanation, this ratio has beentermed the PFC/PC ratio. More generally, it will be appreciated thatcompatible blowing agents and/or surfactants may be substituted for theexemplary compounds without falling outside of the scope of the presentinvention. In any event, the typical PFC/PC ratio will range from about1 to about 60 and more preferably from about 10 to about 50. Forpreferred embodiments the ratio will generally be greater than about 5,10, 20, 25, 30, 40 or even 50. In this respect, FIG. 1 shows a series ofpictures taken of perforated microstructures formed ofphosphatidyicholine (PC) using various amounts of perfluorooctyl bromide(PFC), a relatively high boiling point fluorocarbon as the blowingagent. The PFC/PC ratios are provided under each subset of pictures,i.e. from 1A to 1F. Formation and imaging conditions are discussed ingreater detail in Examples I and II below. With regard to themicrographs, the column on the left shows the intact microstructureswhile the column on the right illustrates cross-sections of fracturedmicrostructures from the same preparations.

As may easily be seen in the FIG. 1, the use of higher PFC/PC ratiosprovides structures of a more hollow and porous nature. Moreparticularly, those methods employing a PFC/PC ratio of greater thanabout 4.8 tended to provide structures that are particularly compatiblewith the dry power formulations and dispersions disclosed herein.Similarly, FIG. 3, a micrograph which will be discussed in more detailin Example XII below, illustrates a preferably porous morphologyobtained by using higher boiling point blowing agents (in this caseperfluorodecalin).

While relatively high boiling point blowing agents comprise onepreferred aspect of the instant invention, it will be appreciated thatmore conventional and unconventional blowing or inflating agents mayalso be used to provide compatible perforated microstructures. Theblowing agent comprises any volatile substance, which can beincorporated into the feed solution for the purpose of producing aperforated foam-like structure in the resulting dry microspheres. Theblowing agent may be removed during the initial drying process or duringa post-production step such as vacuum drying or solvent extraction.Suitable agents include:

-   -   1. Dissolved low-boiling (below 100° C.) agents miscible with        aqueous solutions, such as methylene chloride, acetone, ethyl        acetate, and alcohols used to saturate the solution.    -   2. A gas, such as CO₂ or N₂, or liquid such as Freons, CFCs,        HFAs, PFCs, HFCs, HFBs, fluoroalkanes, and hydrocarbons used at        elevated pressure.    -   3. Emulsions of immiscible low-boiling (below 100° C.) liquids        suitable for use with the present invention are generally of the        formula:        R¹—X—R² or R¹—X        wherein: R¹ or R² is hydrogen, alkyl, alkenyl, alkynl, aromatic,        cyclic or combinations thereof, X is any groups containing        carbon, sulfur, nitrogen, halogens, phosphorus, oxygen and        combinations thereof. Such liquids include: Freons, CFCs, HFAs,        PFCs, HFCs, HFBs, fluoroalkanes, and hydrocarbons.    -   4. Dissolved or dispersed salts or organic substances which can        be removed under reduced pressure by sublimation in a        post-production step, such as ammonium salts, camrphor, etc.    -   5. Dispersed solids which can be extracted after the initial        particle generation using a post-production solvent extraction        step, such particles include latex, etc.

With respect to these lower boiling point inflating agents, they aretypically added to the feed stock in quantities of about 1% to 40% v/vof the surfactant solution. Approximately 15% v/v inflating agent hasbeen found to produce a spray dried powder that may be used to form thestabilized dispersions of the present invention.

Regardless of which blowing agent is ultimately selected, it has beenfound that compatible perforated microstructures may be producedparticularly efficiently using a Büchi mini spray drier (model B-191,Switzerland). As will be appreciated by those skilled in the art, theinlet temperature and the outlet temperature of the spray drier are notcritical but will be of such a level to provide the desired particlesize and to result in a product that has the desired activity of themedicament. In this regard, the inlet and outlet temperatures areadjusted depending on the melting characteristics of the formulationcomponents and the composition of the feed stock. The inlet temperaturemay thus be between 60° C. and 170° C., with the outlet temperatures ofabout 40° C. to 120° C. depending on the composition of the feed and thedesired particulate characteristics. Preferably these temperatures willbe from 90° C. to 120° C. for the inlet and from 60° C. to 90° C. forthe outlet. The flow rate which is used in the spray drying equipmentwill generally be about 3 ml per minute to about 15 ml per minute. Theatomizer air flow rate will vary between values of 25 liters per minuteto about 50 liters per minute. Commercially available spray dryers arewell known to those in the art, and suitable settings for any particulardispersion can be readily determined through standard empirical testing,with due reference to the examples that follow. Of course, theconditions may be adjusted so as to preserve biological activity inlarger molecules such as proteins or peptides.

Though the perforated microstructures are preferably formed usingfluorinated blowing agents in the form of an emulsion, it will beappreciated that nonfluorinated oils may be used to increase the loadingcapacity of active or bioactive agents without compromising themicrostructure. In this case, selection of the nonfluorinated oil isbased upon the solubility of the active or bioactive agent, watersolubility, boiling point, and flash point. The active or bioactiveagent will be dissolved in the oil and subsequently emulsified in thefeed solution. Preferably the oil will have substantial solubilizationcapacity with respect to the selected agent, low water solubility(<10⁻³M), boiling point greater than water and a flash point greaterthan the drying outlet temperature. The addition of surfactants, andco-solvents to the nonfluorinated oil to increase the solubilizationcapacity is also within the scope of the present invention.

In particularly preferred embodiments nonfluorinated oils may be used tosolubilize agents or bioactive agents that have limited solubility inaqueous compositions. The use of nonfluorinated oils is of particularuse for increasing the loading capacity of steroids such asbeclomethasone dipropionate and triamcinolone acetonide. Preferably theoil or oil mixture for solubilizing these clathrate forming steroidswill have a refractive index between 1.36 and 1.41 (e.g. ethyl butyrate,butyl carbonate, dibutyl ether). In addition, process conditions, suchas temperature and pressure, may be adjusted in order to boostsolubility of the selected agent. It will be appreciated that selectionof an appropriate oil or oil mixtures and processing conditions tomaximize the loading capacity of an agent are well within the purview ofa skilled artisan in view of the teachings herein and may beaccomplished without undue experimentation.

Particularly preferred embodiments of the present invention comprisespray drying preparations comprising a surfactant such as a phospholipidand at least one active or bioactive agent. In other embodiments thespray drying preparation may further comprise an excipient comprising ahydrophilic moiety such as, for example, a carbohydrate (i.e. glucose,lactose, or starch) in addition to any selected surfactant. In thisregard various starches and derivatized starches suitable for use in thepresent invention. Other optional components may include conventionalviscosity modifiers, buffers such as phosphate buffers or otherconventional biocompatible buffers or pH adjusting agents such as acidsor bases, and osmotic agents (to provide isotonicity, hyperosmolarity,or hyposmolarity). Examples of suitable salts include sodium phosphate(both monobasic and dibasic), sodium chloride, calcium phosphate,calcium chloride and other physiologically acceptable salts.

Whatever components are selected, the first step in particulateproduction typically comprises feed stock preparation. Preferably theselected drug is dissolved in water to produce a concentrated solution.The drug may also be dispersed directly in the emulsion, particularly inthe case of water insoluble agents. Alternatively, the drug may beincorporated in the form of a solid particulate dispersion. Theconcentration of the active or bioactive agent used is dependent on theamount of agent required in the final powder and the performance of thedelivery device employed (e.g., the fine particle dose for a MDI orDPI). As needed, cosurfactants such as poloxamer 188 or span 80 may bedispersed into this annex solution. Additionally, excipients such assugars and starches can also be added.

In selected embodiments an oil-in-water emulsion is then formed in aseparate vessel. The oil employed is preferably a fluorocarbon (e.g.,perfluorooctyl bromide, perfluorodecalin) which is emulsified using asurfactant such as a long chain saturated phospholipid. For example, onegram of phospholipid may be homogenized in 150 g hot distilled water(e.g., 60° C.) using a suitable high shear mechanical mixer (e.g.,Ultra-Turrax model T-25 mixer) at 8000 rpm for 2 to 5 minutes. Typically5 to 25 g of fluorocarbon is added dropwise to the dispersed surfactantsolution while mixing. The resulting perfluorocarbon in water emulsionis then processed using a high pressure homogenizer to reduce theparticle size. Typically the emulsion is processed at 12,000 to 18,000psi, 5 discrete passes and kept at 50 to 80° C.

The active or bioactive agent solution and perfluorocarbon emulsion arethen combined and fed into the spray dryer. Typically the twopreparations will be miscible as the emulsion will preferably comprisean aqueous continuous phase. While the bioactive agent is solubilizedseparately for the purposes of the instant discussion it will beappreciated that, in other embodiments, the active or bioactive agentmay be solubilized (or dispersed) directly in the emulsion. Insuch-cases, the active or bioactive emulsion is simply spray driedwithout combining a separate drug preparation.

In any event, operating conditions such as inlet and Outlet temperature,feed rate, atomization pressure, flow rate of the drying air, and nozzleconfiguration can be adjusted in accordance with the manufacturer'sguidelines in order to produce the required particle size, andproduction yield of the resulting dry microstructures. Exemplarysettings are as follows: an air inlet temperature between 60° C. and170° C.; an air outlet between 40° C. to 120° C.; a feed rate between 3ml to about 15 ml per minute; and an aspiration air flow of 300 L/min.and an atomization air flow rate between 25 to 50 L/min. The selectionof appropriate apparatus and processing conditions are well within thepurview of a skilled artisan in view of the teachings herein and may beaccomplished without undue experimentation. In any event, the use ofthese and substantially equivalent methods provide for the formation ofhollow porous aerodynamically light microspheres with particle diametersappropriate for aerosol deposition into the lung microstructures thatare both hollow and porous, almost honeycombed or foam-like inappearance. In especially preferred embodiments the perforatedmicrostructures comprise hollow, porous spray dried microspheres.

Along with spray drying, perforated microstructures useful in thepresent invention may be formed by lyophilization. Those skilled in theart will appreciate that lyophilization is a freeze-drying process inwhich water is sublimed from the composition after it is frozen. Theparticular advantage associated with the lyophilization process is thatbiologicals and pharmaceuticals that are relatively unstable in anaqueous solution can be dried without elevated temperatures (therebyeliminating the adverse thermal effects), and then stored in a dry statewhere there are few stability problems. With respect to the instantinvention such techniques are particularly compatible with theincorporation of peptides, proteins, genetic material and other naturaland synthetic macromolecules in particulates or perforatedmicrostructures without compromising physiological activity. Methods forproviding lyophilized particulates are known to those of skill in theart and it would clearly not require undue experimentation to providedispersion compatible microstructures in accordance with the teachingsherein. The lyophilized cake containing a fine foam-like structure canbe micronized using techniques known in the art to provide 3 to 10 μmsized particles. Accordingly, to the extent that lyophilizationprocesses may be used to provide microstructures having the desiredporosity and size they are conformance with the teachings herein and areexpressly contemplated as being within the scope of the instantinvention.

Besides the aforementioned techniques, the perforated microstructures orparticles of the present invention may also be formed using a methodwhere a feed solution (either emulsion or aqueous) containing wallforming agents is rapidly added to a reservoir of heated oil (e.g.perflubron or other high boiling FCs) under reduced pressure. The waterand volatile solvents of the feed solution rapidly boils and areevaporated. This process provides a perforated structure from the wallforming agents similar to puffed rice or popcorn. Preferably the wallforming agents are insoluble in the heated oil. The resulting particlescan then separated from the heated oil using a filtering technique andsubsequently dried under vacuum.

Additionally, the perforated microstructures of the present inventionmay also be formed using a double emulsion method. In the doubleemulsion method the medicarnent is first dispersed in a polymerdissolved in an organic solvent (e.g. methylene chloride) by sonicationor homogenization. This primary emulsion is then stabilized by forming amultiple emulsion in a continuous aqueous phase containing an emulsifiersuch as polyvinylalcohol. Evaporation or extraction using conventionaltechniques and apparatus then removes the organic solvent. The resultingmicrospheres are washed, filtered and dried prior to combining them withan appropriate suspension medium in accordance with the presentinvention

Whatever production method is ultimately selected for production of theperforated microstructures, the resulting powders have a number ofadvantageous properties that make them particularly compatible for usein devices for inhalation therapies. In particular, the physicalcharacteristics of the perforated microstructures make them extremelyeffective for use in dry powder inhalers and in the formation ofstabilized dispersions that may be used in conjunction with metered doseinhalers, nebulizers and liquid dose instillation. As such, theperforated microstructures provide for the effective pulmonaryadministration of bioactive agents.

In order to maximize dispersibility, dispersion stability and optimizedistribution upon administration, the mean geometric particle size ofthe perforated microstructures is preferably about 0.5-50 μm, morepreferably -1-30 μm. It will be appreciated that large particles (i.e.greater than 50 μm) may not be preferred in applications where a valveor small orifice is employed, since large particles tend to aggregate orseparate from a suspension which could potentially clog the device. Inespecially preferred embodiments the mean geometric particle size (ordiameter) of the perforated microstructures is less than 20 μm or lessthan 10 μm. More preferably the mean geometric diameter is less thanabout 7 μm or 5 μm, and even more preferably less than about 2.5 μm.Other preferred embodiments will comprise preparations wherein the meangeometric diameter of the perforated microstructures is between about 1μm and 5 μm. In especially preferred embodiments the perforated,microstructures will comprise a powder of dry, hollow, porousmicrospherical shells of approximately 1 to 10 μm or 1 to 5 μm indiameter, with shell thicknesses of approximately 0.1 μm toapproximately 0.5 μm. It is a particular advantage of the presentinvention that the particulate concentration of the dispersions andstructural matrix components can be adjusted to optimize the deliverycharacteristics of the selected particle size.

As alluded to throughout the instant specification the porosity of themicrostructures may play a significant part is establishingdispersibility (e.g. in DPIs) or dispersion stability (e.g. for MDIs ornebulizers). In this respect, the mean porosity of the perforatedmicrostructures may be determined through electron microscopy coupledwith modern imaging techniques. More specifically, electron micrographsof representative samples of the perforated microstructures may beobtained and digitally analyzed to quantify the porosity of thepreparation. Such methodology, is well known in the art and may beundertaken without undue experimentation.

For the purposes of the present invention, the mean porosity (i.e. thepercentage of the particle surface area that is open to the interiorand/or a central void) of the perforated microstructures may range fromapproximately 0.5% to approximately 80%. In more preferred embodiments,the mean porosity will range from approximately 2% to approximately 40%.Based on selected production parameters, the mean porosity may begreater than approximately, 2%, 5%, 10%, 15%, 20%, 25% or 30% of themicrostructure surface area. In other embodiments, the mean porosity ofthe microstructures may be greater than about 40%, 50%, 60%, 70% or even80%. As to the pores themselves, they typically-range in size from about5 nm to about 400 nm with mean pore sizes preferably in the range offrom about 20 nm to about 200 nm. In particularly preferred embodimentsthe mean pore size will be in the range of from about 50 nm to about 100nm. As may be seen in FIGS. 1A1 to 1F2 and discussed in more detailbelow, it is a significant advantage of the present invention that thepore size and porosity may be closely controlled by careful selection ofthe incorporated components and production parameters.

In this regard, the particle morphology and/or hollow design of theperforated microstructures also plays an important role on thedispersibility or cohesiveness of the dry powder formulations disclosedherein. That is, .it has been surprisingly discovered that the inherentcohesive character of fine powders can be overcome by lowering the vander Waals, electrostatic attractive and liquid bridging forces thattypically exist between dry particles. More specifically, in concordancewith the teachings herein, improved powder dispersibility may beprovided by engineering the particle morphology and density, as well ascontrol of humidity and charge. To that end, the perforatedmicrostructures of the present invention comprise pores, voids, hollows,defects or other interstitial spaces which reduce the surface contactarea between particles thereby minimizing interparticle forces. Inaddition, the use of surfactants such as phospholipids and fluorinatedblowing agents in accordance with the teachings herein may contribute toimprovements in the flow properties of the powders by tempering thecharge and strength of the electrostatic forces as well as moisturecontent.

Most fine powders (e.g. <5 μm) exhibit poor dispersibility which can beproblematic when attempting to deliver, aerosolize and/or package thepowders. In this respect the major forces which control particleinteractions can typically be divided into long and short range forces.Long range forces include gravitational attractive forces andelectrostatics, where the interaction varies as a square of theseparation distance or particle diameter. Important short range forcesfor dry powders include van der Waals interactions, hydrogen bonding andliquid bridges. The latter two short range forces differ from the othersin that they occur where there is already contact between particles. Itis a major advantage of the present invention that these attractiveforces may be substantially attenuated or reduced through the use ofperforated microstructures as described herein.

In an effort to overcome these attractive forces, typical prior art drypowder formulations for DPIs comprise micronized drug particles that aredeposited on large carrier particles (e.g., 30 to 90 μm) such as lactoseor agglomerated units of pure drug particles or agglomeration of finelactose particles with pure drug, since they are more readily fluidizedthan neat drug particles. In addition, the mass of drug required peractuation is typically less than 100 μg and is thus prohibitively toosmall to meter. Hence, the larger lactose particles in prior artformulations function as both a carrier particle for aerosolization anda bulking agent for metering. The use of large particles in theseformulations are employed since powder dispersibility and aerosolizationefficiency improves with increasing increasing particle size as a resultof diminished interparticle forces (French, D. L., Edwards, D. A., sandNiven, R. W., J. Aerosol Sci. 27, 769-783, 1996 which is incorporatedherein by reference). That is, prior art formulations often use largeparticles or carriers to overcome the principle forces controllingdispersibility such as van der Waals forces, liquid bridging, andelectrostatic attractive forces that exists between particles.

Those skilled in the art will appreciate that the van der Waals (VDW)attractive force occurs at short range and depends, at least in part, onthe surface contact between the interacting particles. When two dryparticles approach each other the VDW forces increase with an increasein contact area. For two dry particles, the magnitude of the VDWinteraction force, F⁰ _(vdw), can be calculated using the followingequation:$F_{vdw}^{0} = {\frac{\hslash\omega}{8\pi\quad d_{0}^{2}}\left\lbrack \frac{r_{1}r_{2}}{r_{1} + r_{2}} \right\rbrack}$where h is Planck's constant, a is the angular frequency, d₀ is thedistance at which the adhesional force is at a maximum, and r₁ and r₂are the radii of the two interacting particles. Accordingly, it will beappreciated that one way to minimize the magnitude and strength of theVDW force for dry powders is to decrease the interparticle area ofcontact. It is important to note that the magnitude d₀ is a reflectionof this area of contact. The minimal area of contact between twoopposing bodies will occur if the particles are perfect spheres. Inaddition, the area of contact will be further minimized if the particlesare highly porous. Accordingly, the perforated microstructures of thepresent invention act to reduce interparticle contact and correspondingVDW attractive forces. It is important to note that this reduction inVDW forces is largely a result of the unique particle morphology of thepowders of the present invention rather than an increase in geometricparticle diameter. In this regard, it will be appreciated thatparticularly preferred embodiments of the present invention providepowders having average or small particulates (e.g. mean geometricdiameter <10 μm) exhibiting relatively low VDW attractive forces.Conversely, solid, non-spherical particles such as conventionalmicronized drugs of the same size will exert greater interparticleforces between them and, hence, will exhibit poor powder dispersibility.

Further, as indicated above, the electrostatic force affecting powdersoccurs when either or both of the particles are electrically charged.This phenomenon will result with either an attraction or repulsionbetween particles depending on the similarity or dissimilarity ofcharge. In the simplest case, the electric charges can be describedusing Coulomb's Law. One way to modulate or decrease the electrostaticforces between particles is if either or both particles havenon-conducting surfaces. Thus, if the perforated microstructure powderscomprise excipients, surfactants or active agents that are relativelynon-conducting, then any charge generated in the particle will beunevenly distributed over the surface. As a result, the charge half-lifeof powders comprising non-conducting components will be relatively shortsince the retention of elevated charges is dictated by the resistivityof the material. Resistive or non-conducting components are materialswhich will neither function as an efficient electron donor or acceptor.

Derjaguin et al. (Muller, V. M.; Yushchenko, V. S., and Derjaguin, B.V., J. Colloid Interface Sci. 1980, 77, 115-119), which is incorporatedherein by reference, provide a list ranking molecular groups for theirability to accept or donate an electron. In this regard exemplary groupsmay be ranked as follows:Donor: —NH₂>—OH>—OR>—COOR>—CH₃>—C₆H₅>-halogen>-COOH>—CO>—CN Acceptor:

The present invention provides for the reduction of electrostaticeffects in the disclosed powders though the use of relativelynon-conductive materials. Using the above rankings, preferrednon-conductive materials would include halogenated and/or hydrogenatedcomponents. Materials such as phospholipids and fluorinated blowingagents (which may be retained to some extent in the spray dried powders)are preferred since they can provide resistance to particle charging. Itwill be appreciated that the retention of residual blowing agent (e.g.fluorochemicals) in the particles, even at relatively low levels, mayhelp minimize charging of the perforated microstructures as is typicallyimparted during spray drying and cyclone separation. Based on generalelectrostatic principles and the teachings herein, one skilled in theart would be able to identify additional materials that serve to reducethe electrostatic forces of the disclosed powders without undueexperimentation. Further, if needed, the electrostatic forces can alsobe manipulated and minimized using electrification and chargingtechniques.

In addition to the surprising advantages described above, the presentinvention further provides for the attenuation or reduction of hydrogenand liquid bonding. As known to those skilled in the art, both hydrogenbonding and liquid bridging can result from moisture that is absorbed bythe powder. In general, higher humidities produce higher interparticleforces for hydrophilic surfaces. This is a substantial problem in priorart pharmaceutical formulations for inhalation therapies which tend toemploy relatively hydrophilic compounds such as lactose. However, inaccordance with the teachings herein, adhesion forces due to adsorbedwater can be modulated or reduced by increasing the hydrophobicity ofthe contacting surfaces. One skilled in the art can appreciate that anincrease in particle hydrophobicity can be achieved through excipientselection and/or use a post-production spray drying coating techniquesuch as employed using a fluidized bed. Thus, preferred excipientsinclude hydrophobic surfactants such as phospholipids, fatty acid soapsand cholesterol. In view of the teachings herein, it is submitted that askilled artisan would be able to identify materials exhibiting similardesirable properties without undue experimentation.

In accordance with the present invention, methods such as angle ofrepose or shear index can be used to assess the flow properties of drypowders. The angle of repose is defined as the angle formed when a coneof powder is poured onto a flat surface. Powders having an angle ofrepose ranging from 45° to 20° are preferred and indicate suitablepowder flow. More particularly, powders which possess an angle of reposebetween 33° and 20° exhibit relatively low shear forces and areespecially useful in pharmaceutical preparations for use in inhalationtherapies (e.g. DPIs). The shear index, though more time consuming tomeasure than angle of repose, is considered more reliable and easy todetermine. Those skilled in the art will appreciate that theexperimental procedure outlined by Amidon and Houghton (G. E. Amidon,and M. E. Houghton, Pharm. Manuf., 2, 20, 1985, incorporated herein byreference) can be used estimate the shear index for the purposes of thepresent invention. As described in S. Kocova and N. Pilpel, J. Pharm.Pharmacol. 8, 33-55, 1973, also incorporated herein by reference, theshear index is estimated from powder parameters such as, yield stress,effective angle of internal friction, tensile strength, and specificcohesion. In the present invention powders having a shear index lessthan about 0.98 are desirable. More preferably, powders used in thedisclosed compositions, methods and systems will have shear indices lessthan about 1.1. In particularly preferred embodiments the shear indexwill be less than about 1.3 or even less than about 1.5. Of coursepowders having different shear indices may be used provided the resultin the effective deposition of the active or bioactive agent at the siteof interest.

It will also be appreciated that the flow properties of powders havebeen shown correlate well with bulk density measurements. In thisregard, conventional prior art thinking (C. F. Harwood, J. Pharm. Sci.,60, 161-163, 1971) held that an increase in bulk density correlates withimproved flow properties as predicted by the shear index of thematerial. Conversely, it has surprisingly been found that, for theperforated microstructures of the present invention, superior flowproperties were exhibited by powders having relatively low bulkdensities. That is, the hollow porous powders of the present inventionexhibited superior flow properties over powders substantially devoid ofpores. To that end, it has been found that it is possible to providepowders having bulk densities of less than 0.5 g/cm³ that exhibitparticularly favorable flow properties. More surprisingly, it has beenfound that it is possible to provide perforated microstructure powdershaving bulk densities of less than 0.3 g/cm³ or even less than about 0.1g/cm³ that exhibit excellent flow properties. The ability to produce lowbulk density powders having superior flowability further accentuates thenovel and unexpected nature of the present invention.

In addition, it will be appreciated that the reduced attractive forces(e.g. van der Waals, electrostatic, hydrogen and liquid bonding, etc.)and excellent flowability provided by the perforated microstructurepowders make them particularly useful in preparations for inhalationtherapies (e.g. in inhalation devices such as DPIs, MDIs, nebulizers).Along with the superior flowability, the perforated or porous and/orhollow design of the microstructures also plays an important role in theresulting aerosol properties of the powder when discharged. Thisphenomenon holds true for perforated microstructures aerosolized as asuspension, as in the case of an MDI or a nebulizer, or delivery ofperforated microstructures in dry form as in the case of a DPI. In thisrespect the perforated structure and relatively high surface area of thedispersed microparticles enables them to be carried along in the flow ofgases during inhalation with greater ease for longer distances thannon-perforated particles of comparable size.

More particularly, because of their high porosity, the density of theparticles is significantly less than 1.0 g/cm³, typically less than 0.5g/cm³, more often on the order of 0.1 g/cm³, and as low as 0.01 g/cm³.Unlike the geometric particle size, the aerodynamic particle size,d_(aer), of the perforated microstructures depends substantially on theparticle density, ρ: d_(aer)=d_(geo)ρ, where d_(geo) is the geometricdiameter. For a particle density of 0.1 g/cm³, d_(aer) will be roughlythree times smaller than d_(geo), leading to increased particledeposition into the peripheral regions of the lung and correspondinglyless deposition in the throat. In this regard, the mean aerodynamicdiameter of the perforated microstructures is preferably less than about5 μm, more preferably less than about 3 μm, and, in particularlypreferred embodiments, less than about 2 μm. Such particle distributionswill act to increase the deep lung deposition of the bioactive agentwhether administered using a DPI, MDI or nebulizer. Further, having alarger geometric diameter than aerodynamic diameter brings the particlescloser to the wall of the alveolus thus increasing the deposition ofsmall aerodynamic diameter particles.

As will be shown subsequently in the Examples, the particle sizedistribution of the aerosol formulations of the present invention aremeasurable by conventional techniques such as, for example, cascadeimpaction or by time of flight analytical methods. In addition,determination of the emitted dose from inhalation devices were doneaccording to the proposed U.S. Pharmacopeia method (PharmacopeialPreviews, 22(1996) 3065) which is incorporated herein by reference.These and related techniques enable the “fine particle fraction” of theaerosol, which corresponds to those particulates that are likely toeffectively deposited in the lung, to be calculated. As used herein thephrase “fine particle fraction” refers to the percentage of the totalamount of active medicament delivered per actuation from the mouthpieceof a DPI, MDI or nebulizer onto plates 2-7 of an 8 stage Andersencascade impactor. Based on such measurements the formulations of thepresent invention will preferably have a fine particle fraction ofapproximately 20% or more by weight of the perforated microstructures(w/w), more preferably they will exhibit a fine particle fraction offrom about 25% to 80% w/w, and even more preferably from about 30 to 70%w/w. In selected embodiments the present invention will preferablycomprise a fine particle fraction of greater than about 30%, 40%, 50%,60%, 70% or 80% by weight.

Further, it has also been found that the formulations of the presentinvention exhibit relativety low deposition rates, when compared withprior art preparations, on the induction port and onto plates 0 and 1 ofthe impactor. Deposition on these components is linked with depositionin the throat in humans. More specifically, most commercially availableMDIs and DPIs have simulated throat depositions of approximately 40-70%(w/w) of the total dose, while the formulations of the present inventiontypically deposit less than about 20% w/w. Accordingly, preferredembodiments of the present invention have simulated throat depositionsof less than about 40%, 35%, 30%, 25%, 20%, 15% or even 10% w/w. Thoseskilled in the art will appreciate that significant decrease in throatdeposition provided by the present invention will result in acorresponding decrease in associated local side-effects such as throatirritation and candidiasis.

With respect to the advantageous deposition profile provided by theinstant invention it is well known that MDI propellants typically forcesuspended particles out of the device at a high velocity towards theback of the throat. Since prior art formulations typically contain asignificant percentage of large particles and/or aggregates, as much astwo-thirds or more of the emitted dose may impact the throat. Moreover,the undesirable delivery profile of conventional powder preparations isalso exhibited under conditions of low particle velocity, as occurs withDPI devices. In general, this problem is inherent when aerosolizingsolid, dense, particulates which are subject to aggregation. Yet, asdiscussed above, the novel and unexpected properties of the stabilizeddispersions of the present invention result in surprisingly low throatdeposition upon administration from inhalation device such as a DPI, MDIatomizer or nebulizer.

While not wishing to be bound by any particular theory, it appears thatthe reduced throat deposition provided by the instant invention resultsfrom decreases in particle aggregation and from the hollow and/or porousmorphology of the incorporated microstructures. That is, the hollow andporous nature of the dispersed microstructures slows the velocity ofparticles in the propellant stream (or gas stream in the case of DPIs),just as a hollow/porous whiffle ball decelerates faster than a baseball.Thus, rather than impacting and sticking to the back of the throat, therelatively slow traveling particles are subject to inhalation by thepatient. Moreover, the highly porous nature of the particles allows thpropellant within the perforated microstructure to rapidly leave and theparticle density to drop before impacting the throat. Accordingly, asubstantially higher percentage of the administered bioactive agent isdeposited in the pulmonary air passages where it may be efficientlyabsorbed.

With respect to inhalation therapies, those skilled in the art willappreciate that the perforated microstructure powders of the presentinvention are particularly useful in DPIs. Conventional DPIs, or drypowder inhalers, comprise powdered formulations and devices where apredetermined dose of medicament, either alone or in a blend withlactose carrier particles, is delivered as a fine mist or aerosol of drypowder for inhalation. The medicament is formulated in a way such thatit readily disperses into discrete particles with a size rage between0.5 to 20 μm. The powder is actuated either by inspiration or by someexternal delivery force, such as pressurized air. DPI formulations aretypically packaged in single dose units or they employ reservoir systemscapable of metering multiple doses with manual transfer of the dose tothe device.

DPIs are generally classified based on the dose delivery systememployed. In this respect, the two major types of DPIs comprise unitdose delivery devices and bulk reservoir delivery systems. As usedherein, the term “reservoir” shall be used in a general sense and heldto encompass both configurations unless otherwise dictated by contextualrestraints. In any event, unit dose delivery systems require the dose ofpowder formulation presented to the device as a single unit. With thissystem, the formulation is prefilled into dosing wells which may befoil-packaged or presented in blister strips to prevent moistureingress. Other unit dose packages include hard gelatin capsules. Mostunit dose containers designed for DPIs are filled using a fixed volumetechnique. As a result, there are physical limitations (here density) tothe minimal dose that can be metered into a unit package, which isdictated by the powder flowability and bulk density. Currently, therange of dry powder that can be filled into a unit dose container is inthe range of 5 to 15 mg which corresponds to drug loading in the rangeof 25 to 500 μg per dose. Conversely, bulk reservoir delivery systemsprovide a precise quantity of powder to be metered upon individualdelivery for up to approximately 200 doses. Again like the unit dosesystems, the powder is metered using a fixed volume cell or chamber thatthe powder is filled into. Thus, the density of the powder is a majorfactor limiting the minimal dose that can be delivered with this device.Currently bulk reservoir type DPIs can meter between 200 μg to 20 mgpowder per actuation.

DPIs are designed to be manipulated such that they break open thecapsule/blister or to load bulk powder during actuation, followed bydispersion from a mouthpiece or actuator due to the patient'sinspiration. When the prior art formulations are actuated from a DPIdevice the lactose/drug aggregates are aerosolized and the patientinhales the mist of dry powder. During the inhalation process, thecarrier particles encounter shear forces whereby some of the micronizeddrug particles are separated from the lactose particulate surface. Itwill be appreciated that the drug particles are subsequently carriedinto the lung. The large lactose particles impact the throat and upperairways due to size and inertial force constraints. The efficiency ofdelivery of the drug particles is dictated by their degree of adhesionwith the carrier particles and their aerodynamic property.

Deaggregation can be increased through formulation, process and devicedesign improvements. For example fine particle lactose (FPL) is oftenmixed with coarse lactose carriers, wherein the FPL will occupyhigh-energy binding sites on the carrier particles. This processprovides more passive sites for adhesion of the micronized drugparticles. This tertiary blend with the drug has been shown to providestatistically significant increases in fine particle fraction. Otherstrategies include specialized process conditions where drug particlesare mixed with FPL to produce agglomerated units. In order to furtherincrease particulate deposition, many DPIs are designed to providedeaggregation by passing the dosage form over baffles, or throughtortuous channels that disrupts the flow properties.

The addition of FPL, agglomeration with FPL and specialized devicedesign provides an improvement in the deaggregation of formulations,however, the clinically important parameter is the fine particle dosereceived by the patient. Though improvements in deaggregation can beprovided, a major problem still exists with current DPI devices in thatthere is an increase in respirable dose with an increased inspiratoryeffort. This is a result of an increased fine particle fractioncorresponding to the increased disaggregation of particle agglomeratesas the airflow increases through the inhaler with increasing inspiratoryeffort. Consequently dosing accuracy is compromised, leading tocomplications when the devices are used to administer highly efficaciousdrugs to sensitive populations such as children, adolescents and theelderly. Moreover, the dosing inaccuracy associated with conventionalpreparations could complicate regulatory approval.

In stark contrast, the perforated microstructure powders of the presentinvention obviate many of the difficulties associated with prior artcarrier preparations. That is, an improvement in DPI performance may beprovided by engineering the particle, size, aerodynamics, morphology anddensity, as well as control of humidity and charge. In this respect thepresent invention provides formulations wherein the medicament and theincipients or bulking agents are preferably associated with or comprisethe perforated microstructures. As set forth above, preferredcompositions according to the present invention typically yield powderswith bulk densities less than 0.1 g/cm³ and often less than 0.05 g/cm³.It will be appreciated that providing powders having bulk densities anorder of a magnitude less than conventional DPI formulations allows formuch lower doses of the selected bioactive agent to be filled into aunit dose container or metered via reservoir-based DPIs. The ability toeffectively meter small quantities is of particular importance for lowdose steroid, long acting bronchodilators and new protein or peptidemedicaments proposed for DPI delivery. Moreover, the ability toeffectively deliver particulates without associated carrier particlessimplifies product formulation, filling and reduces undesirable sideeffects.

As discussed above, the hollow porous powders of the present inventionexhibit superior flow properties, as measured by the angle of repose orshear index methods described herein, with respect to equivalent powderssubstantially devoid of pores. That is, superior powder flow, whichappears to be a function of bulk density and particle morphology, isobserved where the powders have a bulk density less than 0.5 g/cm³.Preferably the powders have bulk densities of less than about 0.3 g/cm³,0.1 g/cm³ or even less than about 0.05 g/cm³. In this regard, it istheorized that the perforated microstructures comprising pores, voids,hollows, defects or other interstitial spaces contribute to powder flowproperties by reducing the surface contact area between particles andminimizing interparticle forces. In addition, the use of phospholipidsin preferred embodiments and retention of fluorinated blowing agents mayalso contribute to improvements in the flow properties of the powders bytempering the charge and strength of the electrostatic forces as well asmoisture content.

In addition to the aforementioned advantages, the disclosed powdersexhibit favorable aerodynamic properties that make them particularlyeffective for use in DPIs. More specifically, the perforated structureand relatively high surface area of the microparticles enables them tobe carried along in the flow of gases during inhalation with greaterease and for longer distances than relatively non-perforated particlesof comparable size. Because of their high porosity and low density,administration of the perforated microstructures with a DPI provides forincreased particle deposition into the peripheral regions of the lungand correspondingly less deposition in the throat. Such particledistribution acts to increase the deep lung deposition of theadministered agent which is preferable for systemic administration.Moreover, in a substantial improvement over prior art DPI preparationsthe low-density, highly porous powders of the present inventionpreferably eliminate the need for carrier particles. Since the largelactose carrier particles will impact the throat and upper airways dueto their size, the elimination of such particles minimizes throatdeposition and any associated “gag” effect associated with conventionalDPIs.

Along with their use in a dry powder configuration, it will beappreciated that the perforated microstructures of the present inventionmay be incorporated in a suspension medium to provide stabilizeddispersions. Among other uses, the stabilized dispersions provide forthe effective delivery of bioactive agents to the pulmonary air passagesof a patient using MDIs, nebulizers or liquid dose instillation (LDItechniques).

As with the DPI embodiments, Administration of a bioactive agent usingan MDI, nebulizer or LDI technique may be indicated for the treatment ofmild, moderate or severe, acute or chronic symptoms or for prophylactictreatment. Moreover, the bioactive agent may be administered to treatlocal or systemic conditions or disorders. It will be appreciated that,the precise dose administered will depend on the age and condition ofthe patient, the particular medicament used and the frequency ofadministration, and will ultimately be at the discretion of theattendant physician. When combinations of bioactive agents are employed,the dose of each component of the combination will generally be thatemployed for each component when used alone.

Those skilled in the art will appreciate the enhanced stability of thedisclosed dispersions or suspensions is largely achieved by lowering thevan der Waals attractive forces between the suspended particles, and byreducing the differences in density between the suspension medium andthe particles. In accordance with the teachings herein, the increases insuspension stability may be imparted by engineering perforatedmicrostructures which are then dispersed in a compatible suspensionmedium. As discussed above, the perforated microstructures comprisepores, voids, hollows, defects or other interstitial spaces that allowthe fluid suspension medium to freely permeate or perfuse theparticulate boundary. Particularly preferred embodiments compriseperforated microstructures that are both hollow and porous, almosthoneycombed or foam-like in appearance. In especially preferredembodiments the perforated microstructures comprise hollow, porous spraydried microspheres.

When the perforated microstructures are placed in the suspension medium(i.e. propellant), the suspension medium is able to permeate theparticles, thereby creating a “homodispersion”, wherein both thecontinuous and dispersed phases are indistinguishable. Since the definedor “virtual” particles (i.e. comprising the volume circumscribed by themicroparticulate matrix) are made up almost entirely of the medium inwhich they are suspended, the forces driving particle aggregation(flocculation) are minimized. Additionally, the differences in densitybetween the defined particles and the continuous phase are minimized byhaving the microstructures filled with the medium, thereby effectivelyslowing particle creaming or sedimentation. As such, the perforatedmicrospheres and stabilized suspensions of the present invention areparticularly compatible with many aerosolization techniques, such as MDIand nebulization. Moreover, the stabilized dispersions may be used inliquid dose instillation applications.

Typical prior art suspensions (e.g. for MDIs) comprise mostly solidparticles and small amounts (<1% w/w) of surfactant (e.g. lecithin,Span-85, oleic acid) to increase electrostatic repulsion betweenparticles or polymers to sterically decrease particle interaction. Insharp contrast, the suspensions of the present invention are designednot to increase repulsion between particles, but rather to decrease theattractive forces between particles. The principal forces drivingflocculation in nonaqueous media are van der Waals attractive forces. Asdiscussed above, VDW forces are quantum mechanical in origin, and can bevisualized as attractions between fluctuating dipoles (i.e. induceddipole-induced dipole interactions). Dispersion forces are extremelyshort-range and scale as the sixth power of the distance between atoms.When two macroscopic bodies approach one another the dispersionattractions between the atoms sums up. The resulting force is ofconsiderably longer range, and depends on the geometry of theinteracting bodies.

More specifically, for two spherical particles, the magnitude of the VDWpotential, V_(A), can be approximated by:${V_{A} = {\frac{- A_{eff}}{6\quad H_{0}}\frac{R_{1}R_{2}}{\left( {R_{1} + R_{2}} \right)}}},$where A_(eff) is the effective Hamaker constant which accounts for thenature of the particles and the medium, H₀ is the distance betweenparticles, and R₁ and R₂ are the radii of spherical particles 1 and 2.The effective Hamaker constant is proportional to the difference in thepolarizabilities of the dispersed particles and the suspension medium:A_(eff)=({square root}{square root over (A_(SM))}−{square root}{squareroot over (A_(PART))})², where A_(SM) and A_(PART) are the Hamakerconstants for the suspension medium and the particles, respectively. Asthe suspended particles and the dispersion medium become similar innature, A_(SM) and A_(PART) become closer in magnitude, and A_(eff) andV_(A) become smaller. That is, by reducing the eff differences betweenthe Hamaker constant associated with suspension medium and the Hamakerconstant associated with the dispersed particles, the effective Hamakerconstant (and corresponding van der Waals attractive forces) may bereduced.

One way to minimize the differences in the Hamaker constants is tocreate a “homodispersion”, that is make both the continuous anddispersed phases essentially indistinguishable as discussed above.Besides exploiting the morphology of the particles to reduce theeffective Hamaker constant, the components of the structural matrix(defining the perforated microstructures) will preferably be chosen soas to exhibit a Hamaker constant relatively close to that of theselected suspension medium. In this respect, one may use the actualvalues of the Hamaker constants of the suspension medium and theparticulate components to determine the compatibility of the dispersioningredients and provide a good indication as to the stability of thepreparation. Alternatively, one could select relatively compatibleperforated microstructure components and suspension mediums usingcharacteristic physical values that coincide with measurable Hamakerconstants but are more readily discernible.

In this respect, it has been found that the refractive index values ofmany compounds tend to scale with the corresponding Hamaker constant.Accordingly, easily measurable refractive index values may be used toprovide a fairly good indication as to which combination of suspensionmedium and particle excipients will provide a dispersion having arelatively low effective Hamaker constant and associated stability. Itwill be appreciated that, since refractive indices of compounds arewidely available or easily derived, the use of such values allows forthe formation of stabilized dispersions in accordance with the presentinvention without undue experimentation. For the purpose of illustrationonly, the refractive indices of several compounds compatible with thedisclosed dispersions are provided in Table 1 immediately below: TABLE ICompound Refractive Index HFA-134a 1.172 HFA-227 1.223 CFC-12 1.287CFC-114 1.288 PFOB 1.305 Mannitol 1.333 Ethanol 1.361 n-octane 1.397DMPC 1.43 Pluronic F-68 1.43 Sucrose 1.538 Hydroxyethylstarch 1.54Sodium chloride 1.544

Consistent with the compatible dispersion components set forth above,those skilled in the art will appreciate that, the formation ofdispersions wherein the components have a refractive index differentialof less than about 0.5 is preferred. That is, the refractive index ofthe suspension medium will preferably be within about 0.5 of therefractive index associated with the perforated particles ormicrostructures. It will further be appreciated that, the refractiveindex of the suspension medium and the particles may be measureddirectly or approximated using the refractive indices of the majorcomponent in each respective phase. For the perforated microstructures,the major component may be determined on a weight percent basis. For thesuspension medium, the major component will typically be derived on avolume percentage basis. In selected embodiments of the presentinvention the refractive index differential value will preferably beless than about 0.45, about 0.4, about 0.35 or even less than about 0.3.Given that lower refractive index differentials imply greater dispersionstability, particularly preferred embodiments comprise indexdifferentials of less than about 0.28, about 0.25, about 0.2, about 0.15or even less than about 0.1. It is submitted that a skilled artisan willbe able to determine which excipients are particularly compatiblewithout undue experimentation given the instant disclosure. The ultimatechoice of preferred excipients will also be influenced by other factors,including biocompatibility, regulatory status, ease of manufacture,cost.

As discussed above, the minimization of density differences between theparticles and the continuous phase is largely dependent on theperforated and/or hollow nature of the microstructures, such that thesuspension medium constitutes most of the particle volume. As usedherein, the term “particle volume” corresponds to the volume ofsuspension medium that would be displaced by the incorporatedhollow/porous particles if they were solid, i.e. the volume defined bythe particle boundary. For the purposes of explanation, and as discussedabove, these fluid filled particulate volumes may be referred to as“virtual particles.” Preferably, the average volume: of the bioactiveagent/excipient shell or matrix (i.e. the volume of medium actuallydisplaced by the perforated microstructure) comprises less than 70% ofthe average particle volume (or less than 70% of the virtual particle).More preferably, the volume of the microparticulate matrix comprisesless than about 50%, 40%, 30% or even 20% of the average particlevolume. Even more preferably, the average volume of the shell/matrixcomprises less than about 10%, 5%, 3% or 1% of the average particlevolume. Those skilled in the art will appreciate that, such a matrix orshell volumes typically contributes little to the virtual particledensity which is overwhelmingly dictated by the suspension medium foundtherein. Of course, in selected embodiments the excipients used to formthe perforated microstructure may be chosen so the density of theresulting matrix or shell approximates the density of the surroundingsuspension medium.

It will further be appreciated that, the use of such microstructureswill allow the apparent density of the virtual particles to approachthat of the suspension medium substantially eliminating the attractivevan der Waals forces. Moreover, as previously discussed, the componentsof the microparticulate matrix are preferably selected, as much aspossible given other considerations, to approximate the density ofsuspension medium. Accordingly, in preferred embodiments of the presentinvention, the virtual particles and the suspension medium will have adensity differential of less than about 0.6 g/cm³. That is, the meandensity of the virtual particles (as defined by the matrix boundary)will be within approximately 0.6 g/cm³ of the suspension medium. Morepreferably, the mean density of the virtual particles will be within0.5, 0.4, 0.3 or 0.2 g/cm³ of the selected suspension medium. In evenmore preferable embodiments the density differential will be less thanabout 0.1, 0.05, 0.01, or even less than 0.005 g/cm³.

In addition to the aforementioned advantages, the use of hollow, porousparticles allows for the formation of free-flowing dispersionscomprising much higher volume fractions of particles in suspension. Itshould be appreciated that, the formulation of prior art dispersions atvolume fractions approaching close-packing generally results in dramaticincreases in dispersion viscoelastic behavior. Rheological behavior ofthis type is not appropriate for MDI applications. Those skilled in theart will appreciate that, the volume fraction of the particles may bedefined as the ratio of the apparent volume of the particles (i.e. theparticle volume) to the total volume of the system. Each system has amaximum volume fraction or packing fraction. For example, particles in asimple cubic arrangement reach a maximum packing fraction of 0.52 whilethose in a face centered cubic/hexagonal close packed configurationreach a maximum packing fraction of approximately 0.74. Fornon-spherical particles or polydisperse systems, the derived values aredifferent. Accordingly, the maximum packing fraction is often consideredto be an empirical parameter for a given system.

Here, it was surprisingly found that the porous structures of thepresent invention do not exhibit undesirable viscoelastic behavior evenat high volume fractions, approaching close packing. To the contrary,they remain as free flowing, low viscosity suspensions having little orno yield stress when compared with analogous suspensions comprisingsolid particulates. The low viscosity of the disclosed suspensions isthought to be due, at least in large part, to the relatively; low vander Waals attraction between the fluid-filled hollow, porous particles.As such, in selected embodiments the volume fraction of the discloseddispersions is greater than approximately 0.3. Other embodiments mayhave packing values on the order of 0.3 to about 0.5 or on the order of0.5 to about 0.8, with the higher values approaching a close packingcondition. Moreover, as particle sedimentation tends to naturallydecrease when the volume fraction approaches close packing, theformation of relatively concentrated dispersions may further increaseformulation stability.

Although the methods and compositions of the present invention may beused to form relatively concentrated suspensions, the stabilizingfactors work equally well at much lower packing, volumes and suchdispersions are contemplated as being within the scope of the instantdisclosure. In this regard, it will be appreciated that, dispersionscomprising low volume fractions are extremely difficult to stabilizeusing prior art techniques. Conversely, dispersions incorporatingperforated microstructures comprising a bioactive agent as describedherein are particularly stable even at low volume fractions.Accordingly, the present invention allows for stabilized dispersions,and particularly respiratory dispersions, to be formed and used atvolume fractions less than 0.3. In some preferred embodiments, thevolume fraction is approximately 0.0001-0.3, more preferably 0.001-0.01.Yet other preferred embodiments comprise stabilized suspensions havingvolume fractions from approximately 0.01 to approximately 0.1.

The perforated microstructures of the present invention may also be usedto stabilize dilute suspensions of micronized bioactive agents. In suchembodiments the perforated microstructures may be added to increase thevolume fraction of particles in the suspension, thereby increasingsuspension stability to creaming or sedimentation. Further, in theseembodiments the incorporated microstructures may also act in preventingclose approach (aggregation) of the micronized drug particles. It shouldbe appreciated that, the perforated microstructures incorporated in suchembodiments do not necessarily comprise a bioactive agent. Rather, theymay be formed exclusively of various excipients, including surfactants.

Those skilled in the art will further appreciate that the stabilizedsuspensions or dispersions of the present invention may be prepared bydispersal of the microstructures in the selected suspension medium whichmay then be placed in a container or reservoir. In this regard, thestabilized preparations of the present invention can be made by simplycombining the components in sufficient quantity to produce the finaldesired dispersion concentration. Although the microstructures readilydisperse without mechanical energy, the application of mechanical energyto aid in dispersion (e.g. with the aid of sonication) is contemplated,particularly for the formation of stable emulsions or reverse emulsions.Alternatively, the components may be mixed by simple shaking or othertype of agitation. The process is preferably carried out under anhydrousconditions to obviate any adverse effects of moisture on suspensionstability. Once formed, the dispersion has a reduced susceptibility toflocculation and sedimentation.

As indicated throughout the instant specification, the dispersions ofthe present invention are preferably stabilized. In a broad sense, theterm “stabilized dispersion” will be held to mean any dispersion thatresists aggregation, flocculation or creaming; to the extent required toprovide for the effective delivery of a bioactive agent. While thoseskilled in the art will appreciate that there are several methods thatmay be used to assess the stability of a given dispersion, a preferredmethod for the purposes of the present invention comprises determinationof creaming or sedimentation time using a dynamic photosedimentationmethod. As seen in Example IX and FIG. 2, a preferred method comprisessubjecting suspended particles to a centrifugal force and measuringabsorbance of the suspension as a function of time. A rapid decrease inthe absorbance identifies a suspension with poor stability. It issubmitted that those skilled in the art will be able to adapt theprocedure to specific suspensions without undue experimentation.

For the purposes of the present invention the creaming time shall bedefined as the time for the suspended drug particulates to cream to ½the volume of the suspension medium. Similarly, the sedimentation timemay be defined as the time it takes for the particulates to sediment in½ the volume of the liquid medium. Besides the photosedimentationtechnique described above, a relatively simple way to determine thecreaming time of a preparation is to provide the particulate suspensionin a sealed glass vial. The vials are agitated or shaken to providerelatively homogeneous dispersions which are then set aside and observedusing appropriate instrumentation or by visual inspection. The timenecessary for the suspended particulates to cream to ½ the volume of thesuspension medium (i.e., to rise to the top half of the suspensionmedium), or to sediment within ½ the volume (i.e., to settle in thebottom ½ of the medium), is then noted. Suspension formulations having acreaming time greater than 1 minute are preferred and indicate suitablestability. More preferably, the stabilized dispersions comprise creamingtimes of greater than 1, 2, 5, 10, 15, 20 or 30 minutes. In particularlypreferred embodiments, the stabilized dispersions exhibit creaming timesof greater than about 1, 1.5, 2, 2.5, or 3 hours. Substantiallyequivalent periods for sedimentation times are indicative of compatibledispersions.

As discussed herein, the stabilized dispersions disclosed herein maypreferably be 5 administered to the nasal or pulmonary air passages of apatient via aerosolization, such as with a metered dose inhaler. The useof such stabilized preparations provides for superior dosereproducibility and improved lung deposition as described above. MDIsare well known in the art and could easily be employed foradministration of the claimed dispersions without undue experimentation.Breath activated MDIs, as well as those comprising other types ofimprovements which have been, or will be, developed are also compatiblewith the stabilized dispersions and present invention and, as such, arecontemplated as being with in the scope thereof. However, it should beemphasized that, in preferred embodiments, the stabilized dispersionsmay be administered with-an MDI using a number of different routesincluding, but not limited to, topical, nasal, pulmonary or oral. Thoseskilled in the art will appreciate that, such routes are well known andthat the dosing and administration procedures may be easily derived forthe stabilized dispersions of the present invention.

MDI canisters generally comprise a container or reservoir capable ofwithstanding the vapor pressure of the propellant used such as, aplastic or plastic-coated glass bottle, or preferably, a metal can or,for example, an aluminum can which may optionally be anodized,lacquer-coated and/or plastic-coated, wherein the container is closedwith a metering valve. The metering valves are designed to deliver ametered amount of the formulation per actuation. The valves incorporatea gasket to prevent leakage of propellant through the valve. The gasketmay comprise any suitable elastomeric material such as, for example, lowdensity polyethylene, chlorobutyl, black and whitebutadiene-acrylonitrile rubbers, butyl rubber and neoprene. Suitablevalves are commercially available from manufacturers well known in theaerosol industry, for example, from Valois, France (e.g. DFIO, DF30, DF31/50 ACT, DF60), Bespak plc, LTK (e.g. BK300, BK356) and 3M-NeotechnicLtd., LIK (e.g. Spraymiser).

Each filled canister is conveniently fitted into a suitable channelingdevice or actuator prior to use to form a metered dose inhaler foradministration of the medicament into the lungs or nasal cavity of apatient. Suitable channeling devices comprise for example a valveactuator and a cylindrical or cone-like passage through which medicamentmay be delivered from the filled canister via the metering valve, to thenose or mouth of a patient e.g., a mouthpiece actuator. Metered doseinhalers are designed to deliver a fixed unit dosage of medicament peractuation such as, for example, in the range of 10 to 5000 micrograms ofbioactive agent per actuation. Typically, a single charged canister willprovide for tens or even hundreds of shots or doses.

With respect to MDIs, it is an advantage of the present invention thatany biocompatible suspension medium having adequate vapor pressure toact as a propellant may be used. Particularly preferred suspension mediaare compatible with use in a metered dose inhaler. That is, they will beable to form aerosols upon the activation of the metering valve andassociated release of pressure. In general, the selected suspensionmedium should be biocompatible (i.e. relatively non-toxic) andnon-reactive with respect to the suspended perforated microstructurescomprising the bioactive agent. Preferably, the suspension medium willnot act as a substantial solvent for any components incorporated in theperforated microspheres. Selected embodiments of the invention comprisesuspension media selected from the group consisting of fluorocarbons(including those substituted with other halogens), hydrofluoroalkanes,perfluorocarbons, hydrocarbons, alcohols, ethers or combinationsthereof. It will be appreciated that, the suspension medium may comprisea mixture of various compounds selected to impart specificcharacteristics.

Particularly suitable propellants for use in the MDI suspension mediumsof the present invention are those propellant gases that can beliquefied under pressure at room temperature and, upon inhalation ortopical use, are safe, toxicologically innocuous and free of sideeffects. In this regard, compatible propellants may comprise anyhydrocarbon, fluorocarbon, hydrogen-containing fluorocarbon or mixturesthereof having a sufficient vapor pressure to efficiently form aerosolsupon activation of a metered dose inhaler. Those propellants typicallytermed hydrofluoroalkanes or HFAs are especially compatible. Suitablepropellants include, for example, short chain hydrocarbons, C₁₋₄hydrogen-containing chlorofluorocarbons such as CH₂ClF, CCl₂F₂CHClF,CF₃CHClF, CHF₂CClF₂, CHClFCHF₂, CF₃CH₂Cl, and CClF₂CH₃; C₁₋₄hydrogen-containing fluorocarbons (e.g. HFAs) such as CHF₂CHF₂, CF₃CH₂F,CHF₂CH₃, and CF₃CHFCF₃; and perfluorocarbons such as CF₃CF₃ andCF₃CF₂CF₃. Preferably, a single perfluorocarbon or hydrogen-containingfluorocarbon is employed as the propellant. Particularly preferred aspropellants are 1,1,1,2-tetrafluoroethane (CF₃CH₂F) (HFA-134a) and1,1,1,2,3,3,3-heptafluoro-n-propane (CF₃CHFCF₃) (HFA-227),perfluoroethane, monochlorodifluoromethane, 1,1-difluoroethane, andcombinations thereof. It is desirable that the formulations contain nocomponents that deplete stratospheric ozone. In particular it isdesirable that the formulations are substantially free ofchlorofluorocarbons such as CCl₃F, CCl₂F₂, and CF₃CCl₃.

Specific fluorocarbons, or classes of fluorinated compounds, that areuseful in the suspension media include, but are not limited to,fluoroheptane, fluorocycloheptane, fluorornothylcycloheptane,fluorohexane, fluorocyclohexane, fluoropentane, fluorocyclopentane,fluoromethylcyclopentane, fluorodimethylcyclopentanes,fluoromethylcyclobutane, fluorodimethylcyclobutane,fluorotrimethylcyclobutane, fluorobutane, fluorocyclobutane,fluoropropane, fluoroethers, fluoropolyethers and fluorotriethylamines.It will be appreciated that, these compounds may be used alone or incombination with more volatile propellants. It is a distinct advantagethat such compounds are generally environmentally sound and biologicallynon-reactive.

In addition to the aforementioned fluorocarbons and hydrofluoroalkanes,various chlorofluorocarbons and substituted fluorinated compounds mayalso be used as suspension mediums in accordance with the teachingsherein. In this respect, FC-11 (CCL3F), FC-11B1 (CBrCl2F), FC-11B2(CBr2ClF), FC12B2 (CF2Br2), FC21 (CHCl2F), FC21B1 (CHBrClF), FC-21B2(CHBr2F), FC-31B1 (CH2BrF), FCl13A (CCl3CF3), FC-122 (CClF2CHCl2),FC-123 (CF3CHCl2), FC-132 (CHClFCHClF), FC-133 (CHClFCHF2), FC-141(CH2ClCHClF), FC-141B (CCl2FCH3), FC-142 (CHF2CH2Cl), FC-151(CH2FCH2Cl), FC-152 (CH2FCH2F), FC-1112 (CClF═CClF), FC-1121 (CHCl═CFCl)and FC-1131 (CHCl═CHF) are all compatible with the teachings hereindespite possible attendant environmental concerns. As such, -each ofthese compounds may be used, alone or in combination with othercompounds (i.e. less volatile fluorocarbons) to form the stabilizedrespiratory dispersions of the present invention.

Along with the aforementioned embodiments, the stabilized dispersions ofthe present invention may also be used in conjunction with nebulizers toprovide an aerosolized medicament that may be administered to thepulmonary air passages of a patient in need thereof. Nebulizers are wellknown in the art and could easily be employed for administration of theclaimed dispersions without undue experimentation. Breath activatednebulizers, as well as those comprising other types of improvementswhich have been, or will be, developed are also compatible with thestabilized dispersions and present invention and are contemplated asbeing with in the scope thereof.

Nebulizers work by forming aerosols, that is converting a bulk liquidinto small droplets suspended in a breathable gas. Here, the aerosolizedmedicament to be administered (preferably to the pulmonary air passages)will comprise small droplets of suspension medium associated withperforated microstructures comprising a bioactive agent. In suchembodiments, the stabilized dispersions of the present invention willtypically be placed in a fluid reservoir operably associated with anebulizer. The specific volumes of preparation provided, means offilling the reservoir, etc., will largely be dependent on the selectionof the individual nebulizer and is well within the purview of theskilled artisan. Of course, the present invention is entirely compatiblewith single-dose nebulizers and multiple dose nebulizers.

Traditional prior art nebulizer preparations typically comprise aqueoussolutions of the selected pharmaceutical compound. With such prior artnebulizer preparations, it has long been established that corruption ofthe incorporated therapeutic compound can severely reduce efficacy. Forexample, with conventional aqueous multi-dose nebulizer preparations,bacterial contamination is a constant problem. In addition, thesolubilized medicament may precipitate out, or degrade over time,adversely affecting the delivery profile. This is particularly true oflarger, more labile biopolymers such as enzymes or other types ofproteins. Precipitation of the incorporated bioactive agent may lead toparticle growth that results in a substantial reduction in lungpenetration and a corresponding decrease in bioavailability. Such dosingincongruities markedly decrease the effectiveness of any treatment.

The present invention overcomes these and other difficulties byproviding stabilized dispersions with a suspension medium thatpreferably comprises a fluorinated compound (i.e. a fluorochemical,fluorocarbon or perfluorocarbon). Particularly preferred embodiments ofthe present invention comprise fluorochemicals that are liquid at roomtemperature. As indicated above, the use of such compounds, whether as acontinuous phase or, as a suspension medium, provides several advantagesover prior art liquid inhalation preparations. In this regard, it iswell established that many fluorochemicals have a proven history ofsafety and biocompatibility in the lung. Further, in contrast to aqueoussolutions, fluorochemicals do not negatively impact gas exchangefollowing pulmonary administration. To the contrary, they may actuallybe able to improve gas exchange and, due to their unique wettabilitycharacteristics, are able to carry an aerosolized stream of particlesdeeper into the lung, thereby improving systemic delivery of the desiredpharmaceutical compound. In addition, the relatively non-reactive natureof fluorochemicals acts to retard any degradation of an incorporatedbioactive agent. Finally, many fluorochemicals are also bacteriostaticthereby decreasing the potential for microbial growth in compatiblenebulizer devices.

In any event, nebulizer mediated aerosolization typically requires aninput of energy in order to produce the increased surface area of thedroplets and, in some cases, to provide transportation of the atomizedor aerosolized medicament. One common mode of aerosolization is forcinga stream of fluid to be ejected from a nozzle, whereby droplets areformed. With respect to nebulized administration, additional energy isusually imparted to provide droplets that will be sufficiently small tobe transported deep into the lungs. Thus, additional energy is needed,such as that provided by a high velocity gas stream or a piezoelectriccrystal. Two popular types of nebulizers, jet nebulizers and ultrasonicnebulizers, rely on the aforementioned methods of applying additionalenergy to the fluid during atomization.

In terms of pulmonary delivery of bioactive agents to the systemiccirculation via nebulization, recent research has focused on the use ofportable hand-held ultrasonic nebulizers, also referred to as meteredsolutions. These devices, generally known as single-bolus nebulizers,aerosolize a single bolus of medication in an aqueous solution with aparticle size efficient for deep lung delivery in one or two breaths.These devices fall into three broad categories. The first categorycomprises pure piezoelectric single-bolus nebulizers such as thosedescribed by Mütterlein, et. at., (J. Aerosol Med. 1988; 1:231). Inanother category, the desired aerosol cloud may be generated bymicrochannel extrusion single-bolus nebulizers such as those describedin U.S. Pat. No. 3,812,854. Finally, a third category comprises devicesexemplified by Robertson, et. al., (WO 92/11050) which describes cyclicpressurization single-bolus nebulizers. Each of the aforementionedreferences is incorporated herein in their entirety. Most devices aremanually actuated, but some devices exist which are breath actuated.Breath actuated devices work by releasing aerosol when the device sensesthe patient inhaling through a circuit. Breath actuated nebulizers, mayalso be placed in-line on a ventilator circuit to release aerosol intothe air flow which comprises the inspiration gases for a patient.

Regardless of which type of nebulizer is employed, it is an advantage ofthe present invention that biocompatible nonaqueous compounds may beused as suspension mediums. Preferably, they will be able to formaerosols upon the application of energy thereto. In general, theselected suspension medium should be biocompatible (i.e. relativelynon-toxic) and non-reactive with respect to the suspended perforatedmicrostructures comprising the bioactive agent. Preferred embodimentscomprise suspension media selected from the group consisting offluorochemicals, fluorocarbons (including those substituted with otherhalogens), perfluorocarbons, fluorocarbon/hydrocarbon diblocks,hydrocarbons, alcohols, ethers, or combinations thereof. It will beappreciated that, the suspension medium may comprise a mixture ofvarious compounds selected to impart specific characteristics. It willalso be appreciated that the perforated microstructures are preferablyinsoluble in the suspension medium, thereby providing for stabilizedmedicament particles, and effectively protecting a selected bioactiveagent from degradation, as might occur during prolonged storage in anaqueous solution. In preferred embodiments, the selected suspensionmedium is bacteriostatic. The suspension formulation also protects thebioactive agent from degradation during the nebulization process.

As indicated above, the suspension media may comprise any one of anumber of different compounds including hydrocarbons, fluorocarbons orhydrocarbon/fluorocarbon diblocks. In general, the contemplatedhydrocarbons or highly fluorinated or perfluorinated compounds may belinear, branched or cyclic, saturated or unsaturated compounds.Conventional structural derivatives of these fluorochemicals andhydrocarbons are also contemplated as being within the scope of thepresent invention as well. Selected embodiments comprising these totallyor partially fluorinated compounds may contain one or more hetero-atomsand/or atoms of bromine or chlorine. Preferably, these fluorochemicalscomprise from 2 to 16 carbon atoms and include, but are not limited to,linear, cyclic or polycyclic perfluoroalkanes,bis(perfluoroalkyl)alkenes, perfluoroethers, perfluoroamines,perfluoroalkyl bromides and perfluoroalkyl chlorides such asdichlorooctane. Particularly preferred fluorinated compounds for use inthe suspension medium may comprise perfluorooctyl bromide C₈F₁₇Br (PFOBor perflubron), dichlorofluorooctane C₈F₁₆Cl₂, and the hydrofluoroalkaneperfluorooctyl ethane C₈F₁₇C₂H₅ (PFOE). With respect to otherembodiments, the use of perfluorohexane or perfluoropentane as thesuspension medium is especially preferred.

More generally, exemplary fluorochemicals which are contemplated for usein the present invention generally include halogenated fluorochemicals(i.e. C_(n)F_(2n+1)X, XC_(n)F_(2n)X, where n=2−10, X═Br, Cl or I) and,in particular, 1-bromo-F-butane n-C₄F₉Br, 1-bromo-F-hexane (n-C₆F₁₃Br),1-bromo-F-heptane (n-C₇F₁₅Br), 1,4-dibromo-F-butane and1,6-dibromo-F-hexane. Other useful brominated fluorochemicals aredisclosed in U.S. Pat. No. 3,975,512 to Long and are incorporated hereinby reference. Specific fluorochemicals having chloride substituents,such as perfluorooctyl chloride (n-C₈F₁₇Cl), 1,8-dichloro-F-octane(n-ClC₈F₁₆Cl), 1,6-dichloro-F-hexane (n-ClC₆F₁₂Cl), and1,4-dichloro-F-butane (n-ClC₄F₈Cl) are also preferred.

Fluorocarbons, fluorocarbon-hydrocarbon compounds and halogenatedfluorochemicals containing other linkage groups, such as esters,thioethers and amines are also suitable for use as suspension media inthe present invention. For instance, compounds having the generalformula, C_(n)F_(2n+1)OC_(m)F_(2m+1), orC_(n)F_(2n+1)CH═CHC_(m)F_(2m+1), (as for example C₄F₉CH═CHC₄F₉ (F-44E),i-C₃F₉CH═CHC₆F₁₃ (F-i36E), and C₆F₁₃CH═CHC₆F₁₃ (F-66E)) where n and mare the same or different arid n and m are integers from about 2 toabout 12 are compatible with teachings herein. Usefulfluorochemical-hydrocarbon diblock and triblock compounds include thosewith the general formulas C_(n)F_(2n+1)—C_(m)H_(2m+1) andC_(n)F_(2n+1)C_(m)H_(2m−1), where n=2−12; m=2−16 orC_(p)H_(2p+1)—C_(n)F_(2n)—C_(m)H_(2m+1), where p=1−12, m=1−12 andn=2−12. Preferred compounds of this type include C₈F₁₇C₂H₅, C₆F₁₃C₁₀H₂₁,C₈F₁₇C₈H₁₇, C₆F₁₃CH═CHC₆H₁₃ and C₈F₁₇CH═CHC₁₀H₂₁. Substituted ethers orpolyethers (i.e. XC_(n)F_(2n)OC_(m)F_(2m)X, XCFOC_(n)F_(2n)OCF₂X, wheren and m=1−4, X═Br, Cl or I) and fluorochemical-hydrocarbon etherdiblocks or triblocks (i.e. C_(n)F_(2n+1)—O—C_(m)H_(2m+1), where n=2−10;m=2−16 or C_(p)H_(2p+1)—O—C_(n)F_(2n)—O—C_(m)H_(2m+1), where p=2−12,m=1−12 and n=2−12) may also used as well asC_(n)F_(2n+1)O—C_(m)F_(2m)OC_(p)H_(2p+1), wherein n, m and p are from1-12. Furthermore, depending on the application, perfluoroalkylatedethers or polyethers may be compatible with the claimed dispersions.

Polycyclic and cyclic fluorochemicals, such as C₁₀F₁₈ (F-decain orperfluorodecalin), perfluoroperhydrophenanthrene,perfluorotetramethylcyclohexane (AP-144) and perfluoro n-butyldecalinare also within the scope of the invention. Additional usefulfluorochemicals include perfluorinated amines, such as F-tripropylamine(“FTPA”) and F-tributylamine (“FTBA,”). F-4-methyloctahydroquinolizine(“FMOQ”), F-N-methyl-decahydroisoquinoline (“FMIQ”),F-N-methyldecahydroquinoline (“FHQ”), F-N-cyclohexylpyrrolidine (“FCHP”)and F-2-butyltetrahydrofuran (“FC-75” or “FC-77”). Still other usefulfluorinated compounds include perfluorophenanthrene,perfluoromethyldecalin, perfluorodimethylethylcyclohexane,perfluorodimethyldecalin, perfluorodiethyldecalin,perfluoromethyladamantane, perfluorodimethyladamantane. Othercontemplated fluorochemicals having nonfluorine substituents, such as,perfluorooctyl hydride, and similar compounds having different numbersof carbon atoms are also useful. Those skilled in the art will furtherappreciate that other variously modified fluorochemicals are encompassedwithin the broad definition of fluorochemical as used in the instantapplication and suitable for use in the present invention. As such, eachof the foregoing compounds may be used, alone or in combination withother compounds to form the stabilized dispersions of the presentinvention.

Specific fluorocarbons, or classes of fluorinated compounds, that may beuseful as suspension media include, but are not limited to,fluoroheptane, fluorocycloheptane fluoromethylcycloheptane,fluorohexane, fluorocyclohexane, fluoropentane, fluorocyclopentane,fluoromethylcyclopentane, fluorodimethylcyclopentanes,fluoromethylcyclobutane, fluorodimethylcyclobutane,fluorotrimethylcyclobutane, fluorobutane, fluorocyclobutane,fluoropropane, fluoroethers, fluoropolyethers and fluorotriethylamines.Such compounds are generally environmentally sound and are biologicallynon-reactive.

While any fluid compound capable of producing an aerosol upon theapplication of energy may be used in conjunction with the presentinvention, the selected suspension medium will preferably have a vaporpressure less than about 5 atmospheres and more preferably less thanabout 2 atmospheres. Unless otherwise specified, all vapor pressuresrecited herein are measured at 25° C. In other embodiments, preferredsuspension media compounds will have vapor pressures on the order ofabout 5 torr to about 760 torr, with more preferable compounds havingvapor pressures on the order of from about 8 torr to about 600 torr,while still more preferable compounds will have vapor pressures on theorder of from about 10 torr to about 350 torr. Such suspension media maybe used in conjunction with compressed air nebulizers, ultrasonicnebulizers or with mechanical atomizers to provide effective ventilationtherapy. Moreover, more volatile compounds may be mixed with lower vaporpressure components to provide suspension media having specifiedphysical characteristics selected to further improve stability orenhance the bioavailability of the dispersed bioactive agent.

Other embodiments of the present invention directed to nebulizers willcomprise suspension media that boil at selected temperatures underambient conditions (i.e. 1 atm). For example, preferred embodiments willcomprise suspension media compounds that boil above 0° C., above 5° C.,above 10° C., above 15°, or above 20° C. In other embodiments, thesuspension media compound may boil at or above 25° C. or at or above 30°C. In yet other embodiments, the selected suspension media compound mayboil at or above human body temperature (i.e. 37° C.), above 45° C., 55°C., 65° C., 75° C., 85° C. or above 100° C.

Along with MDIs and nebulizers, it will be appreciated that thestabilized dispersions of the present invention may be used inconjunction with liquid dose instillation or LDI techniques. Liquid doseinstillation involves the direct administration of a stabilizeddispersion to the lung. In this regard, direct pulmonary administrationof bioactive compounds is particularly effective in the treatment ofdisorders especially where poor vascular circulation of diseasedportions of a lung reduces the effectiveness of intravenous drugdelivery. With respect to LDI the stabilized dispersions are preferablyused in conjunction with partial liquid ventilation or total liquidventilation. Moreover, the present invention may further compriseintroducing a therapeutically beneficial amount of a physiologicallyacceptable gas (such as nitric oxide or oxygen) into the pharmaceuticalmicrodispersion prior to, during or following administration.

For LDI, the dispersions of the present invention may be administered tothe lung using a pulmonary delivery conduit. Those skilled in the artwill appreciate the term “pulmonary delivery conduit”, as used herein,shall be construed in a broad sense to comprise any device or apparatus,or component thereof, that provides for the instillation oradministration of a liquid in the lungs. In this respect a pulmonarydelivery conduit or delivery conduit shall be held to mean any bore,lumen, catheter, tube, conduit, syringe, actuator, mouthpiece,endotracheal tube or bronchoscope that provides for the administrationor instillation of the disclosed dispersions to at least a portion ofthe pulmonary air passages of a patient in need thereof. It will beappreciated that the delivery conduit may or may not be associated witha liquid ventilator or gas ventilator. In particularly preferredembodiments the delivery conduit shall comprise an endotracheal tube orbronchoscope.

Here it must be emphasized that the dispersions of the present inventionmay be administered to ventilated (e.g. those connected to a mechanicalventilator) or nonventilated, patients (e.g. those undergoingspontaneous respiration). Accordingly, in preferred embodiments themethods and systems of the present invention may comprise the use orinclusion of a mechanical ventilator. Further, the stabilizeddispersions of the present invention may also be used as a lavage agentto remove debris in the lung, or for diagnostic lavage procedures. Inany case the introduction of liquids, particularly fluorochemicals, intothe lungs of a patient is well known and could be accomplished by askilled artisan in possession of the instant specification without undueexperimentation.

Those skilled in the art will appreciate that suspension mediacompatible with LDI techniques are similar to those set forth above foruse in conjunction with nebulizers. Accordingly, for the purposes of thepresent application suspension media for dispersions compatible with LDIshall be equivalent to those enumerated above in conjunction with use innebulizers. In any event, it will be appreciated that in particularlypreferred LDI embodiments the selected suspension medium shall comprisea fluorochemical that is liquid under ambient conditions.

It will be understood that, in connection with the present invention,the disclosed dispersions are preferably administered directly to atleast a portion of the pulmonary air passages of a mammal. As usedherein, the terms “direct instillation” or “direct administration” shallbe held to mean the introduction of a stabilized dispersion into thelung cavity of a mammal. That is, the dispersion will preferably beadministered through the trachea of a patient and into the lungs as arelatively free flowing liquid passing through a delivery conduit andinto the pulmonary air passages. In this regard, the flow of thedispersion may be gravity assisted or may be afforded by: inducedpressure such as through a pump or the compression of a syringe plunger.In any case, the amount of dispersion administered may be monitored bymechanical devices such as flow meters or by visual inspection.

While the stabilized dispersions may be administered up to thefunctional residual capacity of the lungs of a patient, it will beappreciated that selected embodiments will comprise the pulmonaryadministration of much smaller volumes (e.g. on the order of amilliliter or less). For example, depending on the disorder to betreated, the volume administered may be on the order of 1, 3, 5, 10, 20,50, 100, 200 or 500 milliliters. In preferred embodiments the liquidvolume is less than 0.25 or 0.5 percent FRC. For particularly preferredembodiments, the liquid volume is 0.1 percent FRC or less. With respectto the administration of relatively low volumes of stabilizeddispersions it will be appreciated that the wettability and spreadingcharacteristics of the suspension media (particularly fluorochemicals)will facilitate the even distribution of the bioactive agent in thelung. However, in other embodiments it may be preferable to administerthe suspensions a volumes of greater than 0.5, 0.75 or 0.9 percent FRC.In any event, LDI treatment as disclosed herein represents a newalternative for critically ill patients on mechanical ventilators, andopens the door for treatment of less ill patients with bronchoscopicadministration.

It will also be understood that other components can be included in thestabilized dispersions of the present invention. For example, osmoticagents, stabilizers, chelators, buffers, viscosity modulators, salts,and sugars can be added to fine tune the stabilized dispersions formaximum life and ease of administration. Such components may be addeddirectly to the suspension medium or associated with, or incorporatedin, the perforated microstructures. Considerations such as sterility,isotonicity, and biocompatibility may govern the use of conventionaladditives to the disclosed compositions. The use of such agents will beunderstood to those of ordinary skill in the art and, the specificquantities, ratios, and types of agents can be determined empiricallywithout undue experimentation.

Moreover, while the stabilized dispersions of the present invention areparticularly suitable for the pulmonary administration of bioactiveagents, they may also be used for the localized or systemicadministration of compounds to any location of the body. Accordingly, itshould be emphasized that, in preferred embodiments, the formulationsmay be administered using a number of different routes including, butnot limited to, the gastrointestinal tract, the respiratory tract,topically, intramuscularly, intraperitoneally, nasally, vaginally,rectally, aurally, orally or ocular. More generally, the stabilizeddispersions of the present invention may be used to deliver agentstopically or by administration to a non-pulmonary body cavity. Inpreferred embodiments the body cavity is selected from the groupconsisting of the peritoneum, sinus cavity, rectum, urethra,gastrointestinal tract, nasal cavity, vagina, auditory meatus, oralcavity, buccal pouch and pleura. Among other indications, stabilizeddispersions comprising the appropriate bioactive agent, (e.g. anantibiotic or an anti-inflammatory), may be used to treat infections ofthe eye, sinusitis, infections of the auditory tract and even infectionsor disorders of the gastrointestinal tract. With respect to the latter,the dispersions of the present invention may be used to selectivelydeliver pharmaceutical compounds to the lining of the stomach for thetreatment of H. pylori infections or other ulcer related disorders.

With regard to the perforated microstructure powders and stabilizeddispersions disclosed herein those skilled in, the art will appreciatethat they may be advantageously supplied to the physician or otherhealth care professional, in a sterile, prepackaged or kit form. Moreparticularly, the formulations may be supplied as stable powders orpreformed dispersions ready for administration to the patient.Conversely, they may be provided as separate, ready to mix components.When provided in a ready to use form, the powders or dispersions may bepackaged in single use containers or reservoirs, as well as in multi-usecontainers or reservoirs. In either case, the container or reservoir maybe associated with the selected inhalation or administration device andused as described herein. When provided as individual components (e.g.,as powdered microspheres and as neat suspension medium) the stabilizedpreparations may then be formed at any time prior to use by simplycombining the contents of the containers as directed. Additionally, suchkits may contain a number of ready to mix, or prepackaged dosing unitsso that the user can then administer them as needed.

Although preferred embodiments of the present invention comprise powdersand stabilized dispersions for use in pharmaceutical applications, itwill be appreciated that the perforated microstructures and discloseddispersions may be used for a number of non pharmaceutical applications.That is, the present invention provides perforated microstructures whichhave a broad range of applications where a powder is suspended and/oraerosolized. In particular, the present invention is especiallyeffective where an active or bioactive ingredient must be dissolved,suspended or solubilized as fast as possible. By increasing the surfacearea of the porous microparticles or by incorporation with suitableexcipients as described herein, will result in an improvement indispersibility, and/or suspension stability. In this regard, rapiddispersement applications include, but are not limited to: detergents,dishwasher detergents, food sweeteners, condiments, spices, mineralflotation detergents, thickening agents, foliar fertilizers,phytohormones, insect pheromones, insect repellents, pet repellents,pesticides, fungicides, disinfectants, perfumes, deodorants, etc.

Applications that require finely divided particles in a non-aqueoussuspension media (i.e., solid, liquid or gaseous) are also contemplatedas being within the scope of the present invention. As explained herein,the use of perforated microstructures to provide a “homodispersion”minimizes particle-particle interactions. As such, the perforatedmicrospheres and stabilized suspensions of the present invention areparticularly compatible with applications that require: inorganicpigments, dyes, inks, paints, explosives, pyrotechnic, adsorbents,absorbents, catalyst, nucleating agents, polymers, resins, insulators,fillers, etc. The present invention offers benefits over prior artpreparations for use in applications which require aerosolization oratomization. In such non pharmaceutical uses the preparations can be inthe form of a liquid suspension (such as with a propellant) or as a drypowder. Preferred embodiments comprising perforated microstructures asdescribed herein include, but are not limited to, ink jet printingformulations, powder coating, spray paint, spray pesticides etc.

The foregoing description will be more fully understood with referenceto the following Examples. Such Examples, are, however, merelyrepresentative of preferred methods of practicing the present inventionand should not be read as limiting the scope of the invention.

I Preparation of Hollow Porous Particles of Gentamicin Sulfate bySpray-Drying

40 to 60ml of the following solutions were prepared for spray drying:

50% w/w hydrogenated phosphatidylcholine, E-100-3 (Lipoid KG,Ludwigshafen, Germany)

50% w/w gentamicin sulfate (Amresco, Solon, Ohio)

Perfluorooctylbromide, Perflubron (NMK, Japan)

Deionized water

Perforated microstructures comprising gentamicin sulfate were preparedby a spray drying technique using a B-191 Mini Spray-Drier (Büchi,Flawil, Switzerland) under the following conditions: aspiration: 100%,inlet temperature: 85° C.; outlet temperature: 61° C.; feed pump: 10%;N₂ flow: 2,800 L/hr. Variations in powder porosity were examined as afunction of the blowing agent concentration.

Fluorocarbon-in-water emulsions of perfluorooctyl bromide containing a1:1 w/w ratio of phosphatidylcholine (PC), and gentamicin sulfate wereprepared varying only the PFC/PC ratio. 1.3 grams of hydrogenated eggphosphatidylcholine was dispersed in 25 mL deionized water using anUltra-Turrax mixer (model T-25) at 8000 rpm for 2 to 5 minutes (T=60-70°C.). A range from 0 to 40 grams of perflubron was added dropwise duringmixing (T=60-70° C.). After addition was complete, thefluorocarbon-in-water emulsion was mixed for an additional period of notless than 4 minutes. The resulting coarse emulsions were thenhomogenized under high pressure with an Avestin (Ottawa, Canada)homogenizer at 15,000 psi for 5 passes. Gentamicin sulfate was dissolvedin approximately 4 to 5 mL deionized water and subsequently mixed withthe perflubron emulsion immediately prior to the spray dry process. Thegentamicin powders were then obtained by spray drying using theconditions described above. A free flowing pale yellow powder wasobtained for all perflubron containing formulations. The yield for eachof the various formulations ranged from 35% to 60%.

II Morphology of Gentamicin Sulfate Spray-Dried Powders

A strong dependence of the powder morphology, degree of porosity, andproduction yield was observed as a function of the PFC/PC ratio byscanning electron microscopy (SEM). A series of six SEM micrographsillustrating these observations, labeled 1A1 to 1F1, are shown in theleft hand column of FIG. 1. As seen in these micrographs, the porosityand surface roughness was found to be highly dependent on theconcentration of the blowing agent, where the surface roughness, numberand size of the pores increased with increasing PFC/PC ratios. Forexample, the formulation devoid of perfluorooctyl bromide producedmicrostructures that appeared to be highly agglomerated and readilyadhered to the surface of the glass vial. Similarly, smooth, sphericallyshaped microparticles were obtained when relatively little (PFCIPCratio=1.1 or 2.2) blowing agent was used. As the PFC/PC ratio wasincreased the porosity and surface roughness increased dramatically.

As shown in the right hand column of FIG. 1, the hollow nature of themicrostructures was also enhanced by the incorporation of additionalblowing agent. More particularly, the series of six micrographs labeled1A2 to 1F2 show cross sections of fractured microstructures as revealedby transmission electron microscopy (TEM). Each of these images wasproduced using the same microstructure preparation as was used toproduce the corresponding SEM micrograph in the left hand column. Boththe hollow nature and wall thickness of the resulting perforatedmicrostructures appeared to be largely dependent on the concentration ofthe selected blowing agent. That is, the hollow nature of thepreparation appeared to increase and the thickness of the particle wallsappeared to decrease as the PFC/PC ratio increased. As may be seen inFIGS. 1A2 to 1C2 substantially solid structures were obtained fromformulations containing little or no fluorocarbon blowing agent.Conversely, the perforated microstructures produced using a relativelyhigh PFC/PC ratio of approximately 45 (shown in FIG. 1F 2 proved to beextremely hollow with a relatively thin wall ranging from about 43.5 to261 nm. Both types of particles are compatible for use in the presentinvention.

III Preparation of Spray Dried Gentamicin Sulfate Particles UsingVarious Blowing Agents

40 milliliters of the following solutions were prepared for spraydrying:

50% w/w Hydrogenated Phosphatidylcholine, E100-3 (Lipoid KG,Ludwigshafen, Germany)

50% w/w Gentamicin Sulfate (Amresco, Solon Ohio)

Deionized water.

Blowing Agents:

Perfluorodecalin, FDC (Air products, Allenton Pa.)

Perfluorooctylbromide, Perflubron (Atochem, Paris, France)

Perfluorhexane, PFH (3M, St. Paul, Minn.)

1,1,2-trichlorotrifluoroethane, Freon 113 (Baxter, McGaw Park, Ill.)

Hollow porous microspheres with a model hydrophilic drug, e.g.,gentamicin sulfate, were prepared by spray, drying. The blowing agent inthese formulations consisted of an emulsified fluorochemical (FC) oil.Emulsions were prepared with the following FCs: PFH, Freon 113,Perflubron and FDC. 1.3 grams of hydrogenated egg phosphatidylcholinewas dispersed in 25 mL deionized water using a Ultra-Turrax mixer (modelT-25) at 8000 rpm for 2 to 5 minutes (T=60-70). 25 grams of FC was addeddropwise during mixing (T=60-70° C.). After the addition was complete,the FC-in-water emulsion was mixed for a total of not less than 4minutes. The resulting emulsions were then further processed using anAvestin (Ottawa, Canada) high pressure homogenizer at 15,000 psi and 5passes. Gentamicin sulfate was dissolved in approximately 4 to 5 mLdeionized water and subsequently mixed with the FC emulsion. Thegentamicin powders were obtained by spray drying (Büchi, 191 Mini SprayDryer). Each emulsion was fed at a rate of 2.5 mL/min. The inlet andoutlet temperatures of the spray dryer were 85° C. and 55° C.respectively. The nebulization air and aspiration flows were 2800 L/hrand 100% respectively.

A free flowing pale yellow dry powder was obtained for all formulations.The yield for the various formulations ranged from 35 to 60%. Thevarious gentamicin sulfate powders 5 had a mean volume weighted particlediameters that ranged from 1.52 to 4.91 μm.

IV Effect of Blowing Agent on the Morphology of Gentamicin SulfateSpray-Dried Powders

A strong dependence of the powder morphology, porosity, and productionyield (amount of powder captured in the cyclone) was observed as afunction of the blowing agent boiling point. In this respect the powdersproduced in Example III were observed using scanning electronmicroscopy. Spray drying a fluorochemical (FC) emulsion with a boilingpoint at or below the 55° C. outlet temperature (e.g., perfluorohexane[PFH] or Freon 113), yielded amorphously shaped (shriveled or deflated)powders that contained little or no pores. Whereas, emulsions formulatedwith higher boiling FCs (e.g., perflubron, perfluorodecalin, FDC)produced spherical porous particles. Powders produced with higherboiling blowing agents also had production yields approximately twotimes greater than powders produced using relatively low boiling pointblowing agents. The selected blowing agents and their boiling points areshown in Table II directly below. TABLE II Blowing Agent (bp ° C.) Freon113 47.6 PFH 56 FDC 141 Perflubron 141

Example IV illustrates that the physical characteristics of the blowingagent (i.e., boiling point) greatly influences the ability to provideperforated microparticles. A particular advantage of the presentinvention is the ability to alter the microstructure morphology andporosity by modifying the conditions and nature of the blowing agent.

V Preparation of Spray Dried Albuterol Sulfate Particles Using VariousBlowing Agents

Approximately 185 ml of the following solutions were prepared for spraydrying:

49% w/w Hydrogenated Phosphatidylcholine, E100-3 (Lipoid KG,Ludwigshafen, Germany)

50% w/w Albuterol Sulfate (Accurate Chemical, Westbury, N.Y.)

1% w/w Poloxamer 188, NF grade (Mount Olive, N.J.)

Deionized water.

Blowing Agents:

Perfluorodecalin, FDC (Air products, Allenton Pa.)

Perfluorooctylbromide, Perflubron (Atochem, Paris)

Perfluorobutylethane F4H2 (F-Tech, Japan)

Perfluorotributylamine FTBA (3M, St. Paul, Minn.)

Albuterol sulfate powder was prepared by spray-drying technique by usinga B-191 Mini Spray-Drier (Büchi, Flawil, Switzerland) under thefollowing conditions:

Aspiration: 100%

Inlet temperature: 85° C.

Outlet temperature: 61° C.

Feed pump: 2.5 mL/min.

N₂ flow: 47 L/min.

The feed solution was prepared by mixing solutions A and B prior tospray drying.

Solution A: Twenty grams of water was used to dissolve 1.0 grams ofAlbuterol sulfate and 0.021 grams of poloxamer 188.

Solution B represented an emulsion of a fluorocarbon -in water,stabilized by a phospholipid, which was prepared in the following way.Hydrogenated phosphatidylcholine (1.0 grams) was homogenized in 150grams of hot deionized water (T=50 to 60° C.) using an Ultra-Turraxmixer (model T-25) at 8000 rpm, for 2 to 5 minutes (T=60-70° C.).Twenty-five grams of Perflubron (Atochem, Paris, France) was addeddropwise during mixing. After the addition was complete, theFluorochemical-in-water emulsion was mixed for at least 4 minutes. Theresulting emulsion was then processed using an Avestin (Ottawa, Canada)high-pressure homogenizer at 18,000 psi and 5 passes. Solutions A and Bwere combined and fed into the spray dryer under the conditionsdescribed above. A free flowing, white powder was collected at thecyclone separator as is standard for this spray dryer. The albuterolsulfate powders had mean volume weighted particle diameters ranging from1.28 to 2.77 μm, as determined by an Aerosizer (Amherst ProcessInstruments, Amherst, Mass.). By SEM, the albuterol sulfate/phospholipidspray dried powders were spherical and highly porous.

Example V further demonstrates the wide variety of blowing agents thatmay be used to provide perforated microparticles. A particular advantageof the present invention is the ability to alter the microstructuremorphology and porosity by manipulating the formulation and spray dryingconditions. Furthermore, Example V demonstrates the particle diversityachieved by the present invention and the ability to effectivelyincorporate a wide variety of pharmaceutical agents therein.

VI Preparation of Hollow Porous PVA Particles by Spray Drying aWater-in-oil Emulsion

100 ml of the following solutions were prepared for spray drying:

80% w/w Bis-(2-ethylhexyl) Sulfosuccinic Sodium Salt, (Aerosol OT,Kodak, Rochester, N.Y.)

20% w/w Polyvinyl Alcohol, average molecular weight=30,000-70,000 (SigmaChemicals, St. Louis, Mo.)

Carbon Tetrachloride (Aldrich Chemicals, Milwaukee, Wis.)

Deionized water.

Aerosol OT/polyvinyl alcohol particles were prepared by spray-dryingtechnique using a B-191 Mini Spray-Drier (Büchi, Flawil, Switzerland)under the following conditions:

Aspiration: 85%

Inlet temperature: 60° C.

Outlet temperature: 43° C.

Feed pump: 7.5 mL/min.

N₂ flow: 36 L/min.

Solution A: Twenty grams of water was used to dissolve 500 milligrams ofpolyvinyl alcohol (PVA).

Solution B represented an emulsion of carbon tetrachloride in water,stabilized by aerosol OT, which was prepared in the following way. Twograms of aerosol OT, was dispersed in 80 grams of carbon tetrachlorideusing a Ultra-Turrax mixer (model T-25) at 8000 rpm for 2 to 5 minutes(T=15° to 20° C.). Twenty grams of 2.5% w/v PVA was added dropwiseduring mixing. After the addition was complete, the water-in-oilemulsion was mixed for a total of not less than 4 minutes (T=15° to 20°C.). The resulting emulsion was then processed using an Avestin (Ottawa,Canada) high-pressure homogenizer at 12,000 psi and 2 passes. Theemulsion was then fed into the spray dryer under the conditionsdescribed above. A free flowing, white powder was collected at thecyclone separator as is standard for this spray dryer. The AerosolOT/PVA powder had a mean volume weighted particle diameter of 5.28±3.27μm as determined by an Aerosizer (Amherst Process Instruments, Amherst,Mass.).

Example VI further demonstrates the variety of emulsion systems (here,reverse water-in-oil), formulations and conditions that may be used toprovide perforated microparticles. A particular advantage of the presentinvention is the ability to alter formulations and/or conditions toproduce compositions having a microstructure with selected porosity.This principle is further illustrated in the following example.

VII Preparation of Hollow Porous Polycaprolactone Particles by SprayDrying a Water-in-Oil Emulsion

100 mls of the following solutions were prepared for spray drying:

80% w/w Sorbitan Monostearate, Span 60 (Aldrich Chemicals, Milwaukee,Wis.)

20% w/w Polycaprolactone, average molecular weight=65,000 (AldrichChemicals, Milwaukee, Wis.)

Carbon Tetrachloride (Aldrich Chemicals, Milwaukee, Wis.)

Deionized water.

Span 60/polycaprolactone particles were prepared by spray-dryingtechnique by using a B-191 Mini Spray-Drier (Büchi, Flawil, Switzerland)under the following conditions:

Aspiration: 85%

Inlet temperature: 50° C.

Outlet temperature: 3 8° C.

Feed pump: 7.5 mL/min.

N₂ flow: 36 L/min.

A water-in-carbon tetrachloride emulsion was prepared in the followingmanner. Two grams of Span 60, was dispersed in 80 grams of carbontetrachloride using an Ultra-Turrax mixer (model T-25) at 8000 rpm for 2to 5 minutes (T=15 to 20° C.). Twenty grams of deionized water was addeddropwise during mixing. After the addition was complete, thewater-in-oil emulsion was mixed for a total of not less than 4 minutes(T=15 to 20° C.). The resulting emulsion was then further processedusing an Avestin (Ottawa, Canada) high-pressure homogenizer at 12,000psi and 2 passes. Five hundred milligrams of polycaprolactone was addeddirectly to the emulsion and, mixed until thoroughly dissolved. Theemulsion was then fed into the spray dryer under the conditionsdescribed above. A free flowing, white powder was collected at thecyclone separator as is standard for this dryer. The resulting Span60/polycaprolactone powder had a mean volume weighted particle diameterof 3.15±2.17 μM. Again, the present Example demonstrates the versatilitythe instant invention with regard to the feed stock used to provide thedesired perforated microstructure.

VIII Preparation of Hollow Porous Powder by Spray Drying a Gas-In-WaterEmulsion

The following solutions were prepared with water for injection:

Solution 1:

3.9% w/v m-HES hydroxyethylstarch (Ajinomoto, Tokyo, Japan)

3.25% w/v Sodium chloride (Mallinckrodt, St. Louis, Mo.)

2.83% w/v Sodium phosphate, dibasic (Mallinckrodt, St. Louis, Mo.)

0.42% w/v Sodium phosphate, monobasic (Mallinckrodt, St. Louis, Mo.)

Solution 2:

0.45% w/v Poloxamer 188 (BASF, Mount Olive, N.J.)

1.35% w/v Hydrogenated egg phosphatidylcholine, EPC-3 (Lipoid KG,Ludwigshafen, Germany)

The ingredients of solution I were dissolved in warm water using a stirplate. The surfactants in solution 2 were dispersed in water using ahigh shear mixer. The solutions were combined following emulsificationand saturated with nitrogen prior to spray drying.

The resulting dry, free flowing, hollow spherical product had a meanparticle diameter of 2.6±1.5 μm. The particles were spherical and porousas determined by SEM.

This example illustrates the point that a wide of blowing agents (herenitrogen) may be used to provide microstructures exhibiting the desiredmorphology. Indeed, one of the primary advantages of the presentinvention is the ability to alter formation conditions so as to preservebiological activity (i.e. with proteins), or to produce microstructureshaving selected porosity.

IX Suspension Stability of Gentamicin Sulfate Spray-Dried Powders

The suspension stability was defined as, the resistance of powders tocream in a nonaqueous medium using a dynamic photosedimentation method.Each sample was suspended in Perflubron at a concentration of 0.8 mg/mL.The creaming rates were measured using a Horiba CAPA-700photosedimentation particle size analyzer (Irvine, Calif.) under thefollowing conditions: D (max):  3.00 μm D (min.):  0.30 μm D (Div): 0.10 μm Rotor Speed:  3000 rpm ΔX:   10 mm

The suspended particles were subjected to a centrifugal force and theabsorbance of the suspension was measured as a function of time. A rapiddecrease in the absorbance identifies a suspension with poor stability.Absorbance data was plotted versus time and the area under the curve wasintegrated between 0.1 and 1 min., which was taken as a relativemeasurement of stability. FIG. 2 graphically depicts suspensionstability as a function of PFC/PC ratio or porosity. In this case, thepowder porosity was found to increase with increasing PFC/PC. Maximumsuspension stability was observed with formulations having PFC/PC ratiosbetween 3 to 15. For the most part, these formulations appeared stablefor periods greater than 30 minutes using visual inspection techniques.At points beyond this ratio, the suspensions flocculated rapidlyindicating decreased stability. Similar results were observed using thecream layer ratio method, where it was observed that suspensions withPFC/PC ratios between 3 to 15 had a reduced cream layer thickness,indicating favorable suspension stability.

X Preparation of Hollow Porous Particles of Albuterol Sulfate bySpray-Drying

Hollow porous albuterol sulfate particles were prepared by aspray-drying technique with a B-191 Mini Spray-Drier (Büchi, Flawil,Switzerland) under the following spray conditions: aspiration: 100%,inlet temperature: 85° C.; outlet temperature: 61° C.; feed pump: 10%;N₂ flow: 2,800 L/hr. The feed solution was prepared by mixing twosolutions A and B immediately prior to spray drying.

Solution A: 20g of water was used to dissolve 1 g of albuterol sulfate(Accurate Chemical, Westbury, N.Y.) and 0.021 g of poloxamer 188 NFgrade (BASF, Mount Olive, N.J.).

Solution B: A fluorocarbon-in-water emulsion stabilized by phospholipidwas prepared in the following manner. The phospholipid, 1 g EPC-100-3(Lipoid KG, Ludwig shafen, Germany), was homogenized in 150 g of hotdeionized water (T=50 to 60° C.) using an Ultra-Turrax mixer (modelT-25) at 8000 rpm for 2 to 5 minutes (T=60-70° C.). 25 g ofperfluorooctyl bromide (Atochem, Paris, France) was added dropwiseduring mixing. After the fluorocarbon was added, the emulsion was mixedfor a period of not less than 4 minutes. The resulting coarse emulsionwas then passed through a high pressure homogenizer (Avestin, Ottawa,Canada) at 18,000 psi for 5 passes.

Solutions A and B were combined and fed into the spray-dryer under theconditions described above. A free flowing, white powder was collectedat the cyclone separator. The hollow porous albuterol sulfate particleshad a volume-weighted mean aerodynamic diameter of 1.18±1.42 μm asdetermined by a time-of-flight analytical method (Aerosizer, AmherstProcess Instruments, Amherst, Mass.). Scanning electron microscopy (SEM)analysis showed the powders to be spherical and highly porous. The tapdensity of the powder was determined to be less than 0.1 g/cm³.

This foregoing example serves to illustrate the inherent diversity ofthe present invention as a drug delivery platform capable of effectivelyincorporating any one of a number of pharmaceutical agents. Theprinciple is further illustrated in the next example.

XI Preparation of Hollow Porous Particles of BDP by Spray-Drying

Perforated microstructures comprising beclomethasone dipropionate (BDP)particles were prepared by a spray-drying technique with a B-191 MiniSpray-Drier (Büchi, Flawil, Switzerland) under the following sprayconditions: aspiration: 100%, inlet temperature: 85° C.; outlettemperature: 61° C.; feed pump: 10%; N₂ flow: 2,800 L/hr. The feed stockwas prepared by mixing 0.11 g of lactose with a fluorocarbon-in-wateremulsion immediately prior to spray drying. The emulsion was prepared bythe technique described below.

74 mg of BDP (Sigma, Chemical Co., St. Louis, Mo.), 0.5 g of EPC-100-3(Lipoid KG, Ludwigshafen, Germany), 15mg sodium oleate (Sigma), and 7 mgof poloxamer 188 (BASF, Mount Olive, N.J.) were dissolved in 2 ml of hotmethanol. The methanol was then evaporated to obtain a thin film of thephospholipid/steroid mixture. The phospholipid/steroid mixture was thendispersed in 64 g of hot deionized water (T=50 to 60° C.) using anUltra-Turrax mixer (model T-25) at 8000 rpm for 2 to 5 minutes (T=60-70°C.): 8 g of perflubron (Atochem, Paris, France) was added dropwiseduring mixing. After the addition was complete, the emulsion was mixedfor an additional period of not less than 4 minutes. The resultingcoarse emulsion was then passed through a high pressure homogenizer(Avestin, Ottawa, Canada) at 18,000 psi for 5 passes. This emulsion wasthen used to form the feed stock which was spray dried as describedabove. A free flowing, white powder was collected at the cycloneseparator. The hollow porous BDP particles had a tap density of lessthan 0.1 g/cm³.

XII Preparation of Hollow Porous Particles of Cromolyn Sodium bySpray-Drying

Perforated microstructures comprising cromolyn sodium were prepared by aspray-drying technique with a B-191 Mini Spray-Drier (Büchi, Flawil,Switzerland) under the following spray conditions: aspiration: 100%,inlet temperature: 85bC; outlet temperature: 61° C.; feed pump: 10%; N₂flow:, 2,800 L/hr. The feed solution was prepared by mixing twosolutions A and B immediately prior to spray drying.

Solution A: 20g of water was used to dissolve 1g of cromolyn sodium(Sigma Chemical Co, St. Louis, Mo.) and 0.021 g of poloxamer 188 NFgrade (BASF, Mount Olive, N.J.).

Solution B: A fluorocarbon-in-water emulsion stabilized by phospholipidwas prepared in the following manner. The phospholipid, l g EPC-100-3(Lipoid KG, Ludwigshafen, Germany), was homogenized in 150 g of hotdeionized water (T=50 to 60° C.) using an Ultra-Turrax mixer (modelT-25) at 8000 rpm for 2 to 5 minutes (T=60-70° C.). 27 g ofperfluorodecalin (Air Products, Allentown, Pa.) was added dropwiseduring mixing. After the fluorocarbon was added, the emulsion was mixedfor at least 4 minutes. The resulting coarse emulsion was then passedthrough a high pressure homogenizer (Avestin, Ottawa, Canada) at 18,000psi for 5 passes.

Solutions A and B were combined and fed into the spray dryer under theconditions described above. A free flowing, pale yellow powder wascollected at the cyclone separator. The hollow porous cromolyn sodiumparticles had a volume-weighted mean aerodynamic diameter of 1.23±1.31μm as determined by a time-of-flight analytical method (Aerosizer,Amherst Process Instruments, Amherst, Mass.). As shown in FIG. 3,scanning electron microscopy (SEM) analysis showed the powders to beboth hollow and porous. The tap density of the powder was determined tobe less than 0.1 g/cm³.

XIII Preparation of Hollow Porous Particles of DNase I by Spray-Drying

Hollow porous DNase I particles were prepared by a spray dryingtechnique with a B-191 Mini Spray-Drier (Büchi,. Flawil, Switzerland)under the following conditions: aspiration: 100%, inlet temperature: 80°C.; outlet temperature: 61° C.; feed pump: 10%; N₂ flow: 2,800 L/hr. Thefeed was prepared by mixing two solutions A and B immediately prior tospray drying.

Solution A: 20 g of water was used to dissolve 0.5 gr of human pancreasDNase I (Calbiochem, San Diego Calif.) and 0.012 g of poloxamer 188 NFgrade (BASF, Mount Olive, N.J.).

Solution B: A fluorocarbon-in-water emulsion stabilized by phospholipidwas prepared in the following way. The phospholipid, 0.52 g EPC-100-3(Lipoid KG, Ludwigshafen, Germany), was homogenized in 87 g of hotdeionized water (T=50 to 60° C.) using an Ultra-Turrax mixer (modelT-25) at 8000 rpm for 2 to 5 minutes (T=60-70° C.). 13 g of perflubron(Atochem, Paris, France) was added dropwise during mixing. After thefluorocarbon was added, the emulsion was mixed for at least 4 minutes.The resulting coarse emulsion was then passed through a high pressurehomogenizer (Avestin, Ottawa, Canada) at 18,000 psi for 5 passes.

Solutions A and B were combined and fed into the spray dryer under theconditions described above. A free flowing, pale yellow powder wascollected at the cyclone separator. The hollow porous DNase I particleshad a volume-weighted mean aerodynamic diameter of 1.29±1.40 μm asdetermined by a time-of-flight analytical method (Aerosizer, AmherstProcess Instruments, Amherst, Mass.). Scanning electron microscopy (SEM)analysis showed the powders to be both hollow and porous. The tapdensity of the powder was determined to be less than 0.1 g/cm³.

The foregoing example further illustrates the extraordinarycompatibility of the present invention with a variety of bioactiveagents. That is, in addition to relatively small, hardy compounds suchas steroids, the preparations of the present invention may be formulatedto effectively incorporate larger, fragile molecules such as proteinsand genetic material.

XIV Preparation of Perforated Ink Polymeric Particles by Spray Drying

In the following hypothetical example, finely-divided porous sphericalresin particles which may contain coloring material such as a pigment, adye, etc. are formed using the following formulation in accordance withthe teachings herein: Formulation: Butadiene  7.5 g co-monomer Styrene 2.5 g co-monomer Water  18.0 g carrier Fatty Acid Soap  0.5 gemulsifier n-Dodecyl Mercaptan 0.050 g modifier potassium persulfate0.030 g initiator carbon Black  0.50 g pigment

The reaction is allowed to proceed at 50° C. for 8 hours. The reactionis then terminated by spray drying the emulsion using a high pressureliquid chromatography (HPLC) pump. The emulsion is pumped through a200×0.030 inch i.d. stainless steel tubing into a Niro atomizer portablespray dryer (Niro Atomize, Copenhagen, Denmark) equipped with a twofluid nozzle (0.01″ i.d.) employing the following settings: Hot air flowrate: 39.5 CFM Inlet air temp.: 180° C. Outlet air temperature:  80° C.Atomizer nitrogen flow: 45 L/min, 1,800 psi Liquid feed rate: 33 mL/min

It will be appreciated that unreacted monomers serve as blowing agents,creating the perforated microstructure. The described formulation andconditions yield free flowing porous polymeric particles ranging from0.1-100 μm that may be used-in ink formulations. In accordance with theteachings herein the microparticles have the advantage of incorporatingthe pigment directly into the polymeric matrix. The process allows forthe production of different particle sizes by modifying the componentsand the spray drying conditions with the pigment particle diameterlargely dictated by the diameter of the copolymer resin particles.

XV Andersen Impactor Test for Assessing MDI and DPI Performance

The MDIs and DPIs were tested using commonly accepted pharmaceuticalprocedures. The method utilized was compliant with the United StatePharmacopeia (USP) procedure (Pharmacopeial Previews (1996)22:3065-3098) incorporated herein by reference. After 5 shots to waste,20 shots from the test MDI were made into an Andersen Impactor. Thenumber of shots employed for assessing the DPI formulations was dictatedby the drug concentration and ranged from 10 to 20 actuations.

Extraction procedure. The extraction from all the plates, inductionport, and actuator were performed in closed vials with 10 mL of asuitable solvent. The filter was installed but not assayed, because thepolyacrylic binder interfered with the analysis. The mass balance andparticle size distribution trends indicated that the deposition on thefilter was negligibly small. Methanol was used for extraction ofbeclomethasone dipropionate. Deionized water was used, for albuterolsulfate, and cromolyn sodium. For albuterol MDIs, 0.5 ml of 1 N sodiumhydroxide was added to the plate extract, which was used to convert thealbuterol into the phenolate form.

Quantitation procedure. All drugs were quantitated by absorptionspectroscopy (Beckman DU640 spectrophotometer) relative to an externalstandard curve with the extraction solvent as the blank. Beclomethasonedipropionate was quantitated by measuring the absorption of the plateextracts at 238 nm Albuterol MDIs were quantified by measuring theabsorption of the extracts at 243 nm, while cromolyn sodium wasquantitated using the absorption peak at 326 nm.

Calculation procedure. For each MDI, the mass of the drug in the stem(component-3), actuator (-2), induction port (-1) and plates (0-7) werequantified as described above. Stages-3 and -2 were not quantified forthe DPI since this device was only a prototype. The main interest was toassess the aerodynamic properties of the powder which leaves thisdevice. The Fine Particle Dose and Fine Particle Fraction was calculatedaccording to the USP method referenced above. Throat deposition wasdefined as the mass of drug found in the induction port and on plates 0and 1. The mean mass aerodynamic diameters (MMAD) and geometric standarddiameters (GSD) were evaluated by fitting the experimental cumulativefunction with log-normal distribution by using two-parameter fittingroutine. The results of these experiments are presented in subsequentexamples.

XVI

Preparation of Metered Dose Inhalers Containing Hollow Porous Particles

A pre-weighed amount of the hollow porous particles prepared in ExamplesI, X, XI, and XII were placed into 10 ml aluminum cans, and dried in avacuum oven under the flow of nitrogen for 3-4 hours at 40° C. Theamount of powder filled into the can was determined by the amount ofdrug required for therapeutic effect. After this, the can was crimpsealed using a DF31/50act 50 μl valve (Valois of America, Greenwich,Conn.) and filled with HFA-134a (DuPont, Wilmington, Del.) propellant byoverpressure through the stem. The amount of the propellant in the canwas determined by weighing the can before and after the fill.

XVII Effect of Powder Porosity on MDI Performance

In order to examine the effect powder porosity has upon the suspensionstability and aerodynamic diameter, MDIs were prepared as in Example XVIwith various preparations of perforated microstructures comprisinggentamicin formulations as described in Example I. MDIs containing 0.48wt % spray dried powders in HFA 134a were studied. As set forth inExample I, the spray dried powders exhibit varying porosity. Theformulations were filled in clear glass vials to allow for visualexamination.

A strong dependence of the suspension stability and mean volume weightedaerodynamic diameter was observed -as a function of PFC/PC ratio and/orporosity. The volume weighted mean aerodynamic diameter (VMAD) decreasedand suspension stability increased with increasing porosity. The powdersthat appeared solid and smooth by SEM and TEM techniques had the worstsuspension stability and largest mean aerodynamic diameter. MDIs whichwere formulated with highly porous and hollow perforated microstructureshad the greatest resistance to creaming and the smallest aerodynamicdiameters. The measured VMAD values for the dry powders produced inExample I are shown in Table III immediately below. TABLE III PFC/PCPowder VMAD, μm 0 6.1 1.1 5.9 2.2 6.4 4.8 3.9 18.8 2.6 44.7 1.8

XVIII Comparison of Creaming Rates in Cromolyn Sodium Formulations

A comparison of the creaming rates of the commercial Intal formulation(Rhone-Poulenc Rorer) and spray-dried hollow porous particles formulatedin HFA-134a according to Example XII (i.e. see FIG. 3) is shown in FIGS.4A to 4D. In each of the pictures, taken at 0 seconds, 30 seconds, 60seconds and two hours after shaking, the commercial formulation is onthe left and the perforated microstructure dispersion formed accordancewith the present invention is on the right. Whereas the commercial/Intalformulation shows creaming within 30 seconds of mixing, almost nocreaming is noted in the spray-dried particles after 2 hours.

Moreover, there was little creaming in perforated microstructureformulation after 4 hours (not shown). This example clearly illustratesthe balance in density which can be achieved when the hollow porousparticles are filled with the suspension medium (i.e. in the formationof a homodispersion).

XIX Andersen Cascade Impactor Results for Cromolyn Sodium MDIFormulations

The results of cascade impactor tests for a commercially availableproduct (Intal®, Rhone-Poulenc Rorer) and an analogous spray-driedhollow porous powder in HFA-134a prepared according to Examples XII andXVI are shown below in Table IV. The tests were performed using theprotocol set forth in Example XV. TABLE IV Cromolyn Sodium MDIs FineThroat Particle MMAD Deposition, Fine particle Dose, (GSD) μg fraction,% μg Intal ®, 4.7 ± 0.5 629 24.3 ± 2.1  202 ± 27  CFC (n = 4) (RhonePoulenc)  (1.9 ± 0.06) 800 μg dose Spray dried 3.4 ± 0.2 97 67.3 ± 5.5 200 ± 11  hollow (2.0 ± 0.3) porous powder, HFA (Alliance) (n = 3) 300μg dose

The MDI formulated with perforated microstructures was found to havesuperior aerosol performance compared with Intal®. At a comparable fineparticle dose, the spray dried cromolyn formulations possessed asubstantially higher fine particle fraction (˜67%), and significantlydecreased throat deposition (6-fold), along with a smaller MMAD value.It is important to note that the effective delivery provided for by thepresent invention allowed fort a fine particle dose that wasapproximately the same as the prior art commercial formulation eventhough the amount of perforated microstructures administered (300 μg)was roughly a third of the Intal® dose administered (800 μg).

XX Comparison of Andersen Cascade Impactor Results for Albuterol SulfateMicrospheres Delivered From DPIs and MDIs

The in vitro aerodynamic properties of hollow porous albuterol sulfatemicrospheres as prepared in Example X was characterized using anAndersen Mark II Cascade Impactor (Andersen Sampler, Atlanta, Ga.) andan Amherst Aerosizer (Amherst Instruments, Amherst, Mass.).

DPI testing. Approximately, 300 mcg of spray-dried microspheres wasloaded into a proprietary inhalation device. Activation and subsequentplume generation of the dry powder was achieved by the actuation of 50μl of pressurized HFA 134a through a long induction tube. Thepressurized HFA 134a forced air through the induction tube toward thesample chamber, and subsequently aerosolized a plume of dry powder intothe air. The dry powder plume was then taken in the cascade impactor bymeans of the air flow through drawn through the testing device. A singleactuation was discharged into the aerosizer sample chamber for particlesize analysis. Ten actuations were discharged from the device into theimpactor. A 30 second interval was used between each actuation. Theresults were quantitated as described in Example XV.

MDI testing. A MDI preparation of albuterol sulfate microspheres wasprepared as in Example XVI. A single actuation was discharged into theaerosizer sample chamber for particle size analysis. Twenty actuationswere discharged from the device into the impactor. A 30 second intervalwas used between each actuation. Again, the results were quantitated asdescribed in Example XV.

The results comparing the particle size analysis of the neat albuterolsulfate powder and the albuterol sulfate powder discharged from either aDPI or MDI are shown in Table V below. The albuterol sulfate powderdelivered from the DPI was indistinguishable from the neat powder whichindicates that little or no aggregation had occurred during actuation.On the other hand, some aggregation was observed using an MDI asevidenced by the larger aerodynamic diameter of particles delivered fromthe device. TABLE V Sample Mean Size (μm) % under 5.4 μm 95% under (μm)Neat powder 1.2 100 2.0 MDI 2.4 96.0 5.1 DPI 1.1 100 1.8

Similar results were observed when comparing the two dosage forms usingan Andersen Cascade Impactor (FIG. 5). The spray-dried albuterol sulfatepowder delivered from the DPI had enhanced deep lung deposition andminimized throat deposition when compared with the MDI. The MDIformulation had a fine particle fraction (FPF) of 79% and a fineparticle dose (FPD) of 77 μg/actuation, while the DPI had a FPF of 87%and a FPD of 100 μg/actuation.

FIG. 5 and the Example above exemplifies the excellent flow andaerodynamic properties of the herein described spray-dried powdersdelivered from a DPI. Indeed, one of, the primary advantages of thepresent invention is the ability to produce small aerodynamically lightparticles which aerosolize with ease and which have excellent inhalationproperties. These powders have the unique properties which enable themto be effectively and efficiently delivered from either a MDI or DPI.This principle is further illustrated in the next Example.

XXI Comparison of Andersen Cascade Impactor Results for BeclomethasoneDipropionate Microspheres Delivered From DPIs and MDIs

The in vitro aerodynamic properties of hollow porous beclomethasonedipropionate (BDP) microspheres as prepared in Example XI wascharacterized using an Andersen Mark II Cascade Impactor (AndersenSampler, Atlanta, Ga.) and an Amherst Aerosizer (Amherst Instruments,Amherst, Mass.).

DPI testing. Approximately, 300 μg of spray-dried microspheres wasloaded into a proprietary inhalation device. Activation and subsequentplume generation of the dry powder was achieved by the actuation of 50μl of pressurized HFA 134a through a long induction tube. Thepressurized HFA 134a forced air through the induction tube toward thesample chamber, and subsequently aerosolized a plume of dry powder intothe air. The dry powder plume was then taken in the cascade impactor bymeans of the air flow through drawn through the testing device. A singleactuation was discharged into the aerosizer sample chamber for particlesize analysis. Twenty actuations were discharged from the device intothe impactor. A 30 second interval was used between each actuation.

MDI testing. A MDI preparation of beclomethasone dipropionate (BDP)microspheres was prepared as in Example XVI. A single actuation wasdischarged into the aerosizer sample chamber for particle size analysis.Twenty actuations were discharged from the device into the impactor. A30 second interval was used between each actuation.

The results comparing the particle size analysis of the neat BDP powderand the BDP powder discharged from either a DPI or MDI are shown inTable VI immediately below. TABLE VI Sample Mean Size (μm) % under 5.4μm 95% under (μm) Neat powder 1.3 100 2.1 MDI 2.2 98.1 4.6 DPI 1.2 99.82.2

As with Example XX, the BDP powder delivered from the DPI wasindistinguishable from the neat powder which indicates that little or noaggregation had occurred during actuation. On the other hand, someaggregation was observed using an MDI as evidenced by the largeraerodynamic diameter of particles delivered from the device.

The spray-dried BDP powder delivered from the DPI had enhanced deep lungdeposition and minimized throat deposition when compared with the MDI.The MDI formulation had a fine particle fraction (FPF) of 79% and a fineparticle dose (FPD) of 77 μg/actuation, while the DPI had a FPF of 87%and a FPD of 100 μg/actuation.

This foregoing example serves to illustrate the inherent diversity ofthe present invention as a drug delivery platform capable of effectivelyincorporating any one of a number of pharmaceutical agents andeffectively delivered from various types of delivery devices (here MDIand DPI) currently used in the pharmaceutical arena. The excellent flowand aerodynamic properties of the dry powders shown in the proceedingexamples is further exemplified in the next example.

XXII Comparison of Andersen Cascade Impactor Results for AlbuterolSulfate Microspheres and Ventolin Rotacaps® from a Rotahaler® Device

The following procedure was followed to compare the inhalationproperties of Ventolin Rotocaps® (a commercially available formulation)vs. albuterol sulfate hollow porous microspheres formed in accordancewith the present invention. Both preparations were discharged from aRotohaler® device into an 8 stage Andersen Mark II cascade impactoroperated at a flow of 60 L/min. Preparation of the albuterol sulfatemicrospheres is described in Example X with albuterol sulfate depositionin the cascade impactor analyzed as described in Example XV.Approximately 300 μg of albuterol sulfate microspheres were manuallyloaded into empty Ventolin Rotocap® gelatin capsules. The proceduredescribed in the package insert for loading and actuating drug capsuleswith a Rotohaler® device was followed. Ten actuations were dischargedfrom the device into the impactor. A 30 second interval was used betweeneach actuation.

The results comparing the cascade impactor analysis of VentolinRotocaps® and hollow porous albuterol sulfate microspheres dischargedfrom a Rotohaler® device are shown in Table VI immediately below. TABLEVII MMAD Fine Particle Fine Particle Dose Sample (GSD) Fraction %(mcg/dose) Ventolin Rotacaps ® 7.869 20 15 (n = 2) (1.6064) AlbuterolSulfate 4.822 63 60 Microspheres (n = 3) (1.9082)

The hollow porous albuterol sulfate powder delivered from the Rotohaler®device had a significantly higher, fine particle fraction (3-fold) and asmaller MMAD value as compared with Ventolin Rotocaps®. In this regard,the commercially available Ventolin Rotocap® formulation had a fineparticle fraction (FPF) of 20% and a fine particle dose (FPD) of 15μg/actuation, whereas the hollow porous albuterol sulfate microsphereshad a FPF of 63% and a FPD of 60 μg/actuation.

The example above exemplifies the excellent flow and aerodynamicproperties of the spray-dried powders delivered from a Rotahaler®device. Moreover, this example demonstrates that fine powders can beeffectively delivered without carrier particles.

XXIII Nebulization of Porous Particulate Structures ComprisingPhospholipids and Cromolyn sodium in Perfluorooctylethane Using aMicroMist™ Nebulizer

Forty milligrams of the, lipid based microspheres containing 50%cromolyn sodium by weight (as from Example XII) were dispersed in 10 mlperfluorooctylethane (PFOE) by shaking, forming a suspension. Thesuspension was nebulized until the fluorocarbon liquid was delivered orhad evaporated using a MicroMist™ (DeVilbiss) disposable nebulizer usinga PulmoAide® air compressor (DeVilbiss). As described above in ExampleXV, an Andersen Cascade Impactor was used to measure the resultingparticle size distribution. More specifically, cromolyn sodium contentwas measured by UV adsorption at 326 nm. The fine particle fraction isthe ratio of particles deposited in stages 2 through 7 to thosedeposited in all stages of the impactor. The fine particle mass is theweight of material deposited in stages 2 through 7. The deep lungfraction is the ratio of particles deposited in stages 5. through 7 ofthe impactor (which correlate to the alveoli) to those deposited in allstages. The deep lung mass is the weight of material deposited in stages5 through 7. Table VIII immediately below provides a summary of theresults. TABLE VIII fine particle deep lung Fine particle fraction massdeep lung fraction mass 90% 6 mg 75% 5 mg

XXIV Nebulization of Porous Particulate Structures ComprisingPhospholipids and Cromolyn Sodium in Perfluorooctylethane Using aRaindrop® Nebulizer

A quantity of lipid based microspheres containing 50% cromolyn sodium,as from Example XII, weighing 40 mg was dispersed in 10 mlperfluorooctylethane (PFOE) by shaking, thereby forming a suspension.The suspension was nebulized until the fluorocarbon liquid was deliveredor had evaporated using a Raindrop® disposable nebulizer (NellcorPuritan Bennet) connected to a PulmoAide® air compressor (DeVilbiss). AnAndersen Cascade Impactor was used to measure the resulting particlesize distribution in the manner described in Examples XV and XXIII.Table IX immediately below provides a summary of the results. TABLE IXfine particle deep lung Fine particle fraction mass Deep lung fractionmass 90% 4 mg 80% 3 mg

XXV Nebulization of Aqueous Cromolyn Sodium Solution

The contents of plastic vial containing a unit dose inhalation solutionof 20 mg of cromolyn sodium in 2 ml purified water (Dey Laboratories)was nebulized using a MicroMist™ disposable nebulizer (DeVilbiss) usinga PulmoAide® air compressor (DeVilbiss). The cromolyn sodium solutionwas nebulized for 30 minutes. An Andersen Cascade Impactor was used tomeasure the resulting size distribution of the nebulized particles, bythe method described above in Example XV. Table X immediately belowprovides a summary of the results. TABLE X fine particle Deep fineparticle fraction mass Deep lung fraction lung mass 90% 7 mg 60% 5 mg

With regard to the instant results, it will be appreciated that, theformulations nebulized from fluorocarbon suspension mediums in ExamplesXXIII and XXIV provided a greater percentage of deep lung depositionthan the aqueous solution. Such high deposition rates deep in the lungis particularly desirable when delivering agents to the systemiccirculation of a patient.

Those skilled in the art will further appreciate that the presentinvention may be embodied in other specific forms without departing fromthe spirit or central attributes thereof In that the foregoingdescription of the present invention discloses only exemplaryembodiments thereof, it is to be understood that, other variations arecontemplated as being within the scope of the present invention.Accordingly, the present invention is not limited to the particularembodiments which have been described in detail herein. Rather,reference should be made to the appended claims as indicative of thescope and content of the invention.

1. (canceled)
 2. A composition comprising microspheres, wherein saidmicrospheres have a wall thickness of 100 to 500 nm, and a bulk densityof no more than 0.1 g/cm³.
 3. The composition according to claim 2,wherein the mean geometric particle size of said microspheres is lessthan 20 μm.
 4. A composition comprising microspheres, wherein saidmicrospheres have a wall thickness of 43.5 to 261 nm.
 5. The compositionaccording to claim 2 wherein the walls of said microspheres comprisealbumin.
 6. The composition according to claim 2 obtainable byspray-drying a wall-forming material in combination with a blowingagent.
 7. The composition according to claim 2 wherein said microspherescomprise a bioactive agent.
 8. The composition according to claim 7,wherein said microspheres comprise a protein or peptide.
 9. Thecomposition according to claim 7, wherein said microspheres comprise anactive agent selected from the group consisting of insulin, growthhormone and interferon.
 10. An inhaler comprising an inhalableformulation of microspheres wherein said microspheres have a wallthickness of 100 to 500 nm, and a bulk density of no more than 0.1 g/cm³and wherein said microspheres comprise a bioactive agent.
 11. Theinhaler according to claim 10, wherein the formulation comprises themicrospheres as the sole or the predominant component thereof.
 12. Amethod for pulmonary administration of a bioactive agent wherein saidmethod comprises the administration to the lungs of a composition whichcomprises microspheres having a wall thickness of 100 to 500 nm and abulk density of no more than 0.1 g/cm³, wherein said microspheresfurther comprise a bioactive agent.
 13. (previously presented) Themethod according to claim 12, wherein the mean geometric diameter ofsaid microspheres is less than 20 μm.
 14. A method for pulmonaryadministration of a bioactive agent wherein said method comprises theadministration to the lungs of a composition which comprisesmicrospheres having a wall thickness of 43.5 to 261 nm and a bulkdensity of no more than 0.1 g/cm³, wherein said microspheres furthercomprise a bioactive agent.
 15. The method according to claim 12,wherein the walls of said microspheres comprise albumin.
 16. The methodaccording to claim 12, wherein said microspheres are obtainable byspray-drying a wall-forming material, in combination with a blowingagent.
 17. The method according to claim 12, wherein said microspherescomprise a protein or peptide.
 18. The method according to claim 12,wherein said microspheres contain a bioactive agent selected from thegroup consisting of insulin, growth hormone and interferon.
 19. A methodfor diagnosis wherein said method comprises administering to a patientin need of such diagnosis, a composition which comprises microsphereshaving a wall thickness of 100 to 500 nm and a bulk density of no morethan 0.1 g/cm³.
 20. The method according to claim 19, wherein the meangeometric diameter of said microspheres is less than 20 μm.
 21. A methodfor diagnosis wherein said method comprises administering to a patientin need of such diagnosis, a composition which comprises microsphereshaving a wall thickness of 43.5 to 261 nm and a bulk density of no morethan 0.1 g/cm³.
 22. The method according to claim 19, wherein the wallsof said microspheres comprise albumin.
 23. The method according to claim19, wherein said microspheres are obtainable by spray-drying awall-forming material, in combination with a blowing agent.
 24. A methodfor preparing microparticles, wherein said method comprises spray-dryingwall-forming materials and wherein said method further comprisesinclusion of a blowing agent in the feedstock for spray-drying.
 25. Themethod according to claim 24, wherein said blowing agent is selectedfrom the group consisting of ammonium acetate, ammonium carbonate, andacids.
 26. The method according to claim 24, wherein said wall-formingmaterial is albumin.
 27. A composition comprising microspheres, whereinsaid microspheres have a wall thickness of 100 to 500 nm, and a bulkdensity of no more than 0.3 g/cm³.
 28. The composition according toclaim 2 wherein the bulk density is no more than 0.05 g/cm³.